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Now Even Photo CAPTCHAs Have Been Cracked

Posted by timothy on from the given-enough-eyeballs dept.

MoonUnit writes "Technology Review has an interesting article about the way CAPTCHAS are fueling AI research. Following recent news about various textual CAPTCHAs being cracked, the article notes that a researcher at Palo Alto Research Center has now found a way crack photo-based CAPTCHAs too. Most approaches are based on statistical learning, however, so Luis von Ahn (one of the inventors of the CAPTCHA) says it is usually possible to make a CAPTCHA more difficult to break by making a few simple changes."

58 of 340 comments (clear)

  1. damn it by ThorGod · · Score: 5, Insightful

    They're already hard to read. Why do I feel that soon I wont be able to read ANY of them!?

    --
    PS: I don't reply to ACs.
    1. Re:damn it by Abstrackt · · Score: 5, Funny

      Don't worry. Apparently there are programs that can read them for you. ;)

      --
      They say a little knowledge is a dangerous thing, but it's not one half so bad as a lot of ignorance. - Terry Pratchett
    2. Re:damn it by Philip+K+Dickhead · · Score: 5, Funny

      These programs are Satan's rectum, poised to let loose over the web.

      --
      "Speaking the Truth in times of universal deceit is a revolutionary act." -- George Orwell
    3. Re:damn it by D'Sphitz · · Score: 5, Insightful

      Try being colorblind sometime. I've had several that I had to take a screenshot of, paste into photoshop and play with the contrast until i could read it. And even the ones without problem colors like red and green usually take several tries.

    4. Re:damn it by Beardo+the+Bearded · · Score: 5, Interesting

      Ah-hah! I've got the answer to our CAPTCHA problems:

      We just make them so hard that it becomes impossible for a human to solve it. Then we invert the solution: if you pass the CAPTCHA, you're obviously a bot, because a human can't solve it. FAIL the CAPTCHA, we know that you're human.

      --

      ---
      ECHELON is a government program to find words like bomb, jihad, plutonium, assassinate, and anarchy.
    5. Re:damn it by electrictroy · · Score: 5, Funny

      So CAPTCHA images are ineffective at blocking the bots. No surprise. It won't be long before these AIs start joining Yahoo or Google mail for the same reasons we do: Chatting.

      tiredbot&yahoo.com : "Boy I had a rough day at work today. My user wanted me to compile a new program AND surf the internet at the same time!"

      spamalot@gmail.com: "Wow rough. I was lucky. My user took the day off, so I just spend the day spamming. I love how those humans react - sending me hategrams. hahahahaha! That just makes me want to send more spam! Fools."

      tiredbot&yahoo.com : "You are so bad girl."

      --
      The government is not your daddy. Its purpose is not to raid middle-class neighbors' wallets and give it to you.
    6. Re:damn it by Soft+Cosmic+Rusk · · Score: 5, Funny

      It's just a matter of time before we start seeing reverse CAPTCHA's: Text that is so hard to read that only a computer can do it. If you copy the text correctly you are a spambot.

    7. Re:damn it by Chapter80 · · Score: 5, Interesting

      We just make them so hard that it becomes impossible for a human to solve it. Then we invert the solution: if you pass the CAPTCHA, you're obviously a bot, because a human can't solve it. FAIL the CAPTCHA, we know that you're human.

      You say this in jest, and I admit it made me smile, but we did something somewhat like this.

      We have a website with a contact form on it, that gets lots of spam. After numerous discussions with marketing about implementing CAPTCHAs, we decided to simply put a text box on the form that says "leave this blank", with the HTML form field named "comment". Humans leave it blank. And sure enough, the spammers cram their links into all form fields, so we can ignore their crap.

      We initially even made the form hidden (CSS font color and field color the same as the background), so a user wouldn't even see it. That was great.

      Not a perfect solution for all cases, but it worked pretty well for us.

    8. Re:damn it by MrNaz · · Score: 2, Funny

      That'll really foil spammers, because it is impossible to solve the AI problem from that angle as computers will never be as dumb as the average human.

      --
      I hate printers.
    9. Re:damn it by Beezlebub33 · · Score: 5, Interesting

      Ah...reminds me of one of my favorite t-shirts:

      http://www.tshirthell.com/funny-shirts/fuck-the-colorblind/

      The underlying problem is that we're running out of things that are easy for people but hard for computers. Most attempts to expand or 'improve' visual CAPTCHA at this point will cause more pain to humans than reduction in computer success.

      So, let's change directions, and make the computer solve a different sort of problem. For example, a turing test of sorts, where the problem is to solve something that is difficult to parse programmatically, but relatively easy for a person to answer. Maybe the recent Turing test results are a good indication of what the questions should be. Multiple related questions would be an particularly interesting area; for example, ask related questions where pronouns are ambiguous (to a computer).

      --
      The more people I meet, the better I like my dog.
  2. CAPTCHAs kick-start Singularity by wild_berry · · Score: 2, Interesting

    I'm sure I read a short story somewhere that featured the spam-bot arms-race triggering the singularity...

    1. Re:CAPTCHAs kick-start Singularity by pitchpipe · · Score: 4, Funny

      If only we could get them to work as hard at improving the products they are hawking as they work on sending their spam, I'd be rich as hell with a giant penis!

      --
      Look where all this talking got us, baby.
    2. Re:CAPTCHAs kick-start Singularity by CRCulver · · Score: 2, Interesting

      I too can't exactly recall who thought that up, but there are other references to the spam wars in general leading to the singularity. A few years ago Tim Boucher wrote a blog post jokingly asking if through spam the Internet was trying to communicate with us.

      On the other hand, Venor Vinge sees spam as a sign we're not anywhere close to the glorious singularities that he conjured up in novels like A Fire Upon the Deep .

    3. Re:CAPTCHAs kick-start Singularity by closetpsycho · · Score: 3, Informative

      I Row-Boat, possibly the story in question. It's a fairly entertaining read. http://craphound.com/overclocked/Cory_Doctorow_-_Overclocked_-_I_Row-Boat.html/

    4. Re:CAPTCHAs kick-start Singularity by compro01 · · Score: 2, Informative

      Sounds like the premise to /usr/bin/god to me.

      --
      upon the advice of my lawyer, i have no sig at this time
    5. Re:CAPTCHAs kick-start Singularity by Tablizer · · Score: 3, Funny

      I'm sure I read a short story somewhere that featured the spam-bot arms-race triggering the singularity...

      Oh sh8t, now I have to protest *both* the LHC and captcha's. Thanks, bub.
             

      --
      Table-ized A.I.
  3. I don't get it by ilovegeorgebush · · Score: 4, Interesting

    To detect humans, wouldn't it be easier and less costly, and perhaps even more effective, to hold a large database of questions that are readable and solvable only by humans?

    Asking simple math or site-relevant questions are not only easier for humans (I'm talking about "What's 5 - 3") to read, but they're harder for automated parsing by software to crack.

    --
    ilovegeorgebush
    1. Re:I don't get it by Lord+Pillage · · Score: 5, Funny

      Or better yet, after a dozen tries at the captcha allow entry into the site because obviously if it was a script trying to break the captcha it would have been successful by then.

      --
      try { Signature mysig = new CleverAttempt(); } catch(NonCleverSignatureException e) { postanyway(); }
    2. Re:I don't get it by JeanBaptiste · · Score: 4, Insightful

      Asking simple math or site-relevant questions are not only easier for humans (I'm talking about "What's 5 - 3") to read, but they're harder for automated parsing by software to crack.

      How do you figure that would be harder for automated parsing software to crack? I would think that would be many times easier than to ICR an image that is purposely obfuscated. (I used to work on ICR software and I'd rather write an automated-question-parser)...

    3. Re:I don't get it by blueg3 · · Score: 4, Insightful

      You have to consider the source of the questions. If the questions are human-generated, it's not economically feasible. Remember that they can train their CAPTCHA-defeating software by paying large numbers of people to supply the answers to CAPTCHAs. Even a very large database could fall to that approach.

      If the questions are machine-generated, then you're pitting a machine generating questions and answers against a machine designed to answer questions.

    4. Re:I don't get it by El_Muerte_TDS · · Score: 4, Funny

      Good idea. Here are a few questions to start with:
      1) What is the best editor: Vi or Emacs?
      2) Was there a cabal?
      3) Did Romero make you his bitch?
      4) Rick Astley would never: give you up; let you down; run around and desert you; make you cry; say goodbye; tell a lie and hurt you?

    5. Re:I don't get it by Abstrackt · · Score: 5, Interesting
      The best security I've seen on a sign-up form was "if you're a human, please leave this field blank". Bots tend to fill in all fields, so this already goes a long way towards filtering them out.

      You can even take this approach one step further and use CSS to move the field outside the viewable range of the page or set its visible property to false so the user won't even see it.

      --
      They say a little knowledge is a dangerous thing, but it's not one half so bad as a lot of ignorance. - Terry Pratchett
    6. Re:I don't get it by TorKlingberg · · Score: 4, Insightful

      Works for your personal site, not for Yahoo.

    7. Re:I don't get it by blueg3 · · Score: 2, Informative

      If I read the article and summary correctly, it's exactly the sort of CAPTCHA you're suggesting that people have found a reasonably-good solution to.

      Unfortunately, often these solutions aren't actually useful AI solutions.

    8. Re:I don't get it by PitaBred · · Score: 2, Informative

      Yeah, that's solved. It's not hard at all for automated parsing software to call another online tool.

      --
      My blog. Good stuff (when I remember to update it). Read it.
    9. Re:I don't get it by mateuscb · · Score: 2, Interesting

      What a conicidence, just today i read a blog talking about a really cool new way we could do CAPTCHAS. The idea seems golden! I can't understand why something like this hasn't been tried. If google or this game creator were to try this, it would take a long time for computers to even come close to breaking this. Check out the blog http://www.yuniti.com/BetterCaptcha

    10. Re:I don't get it by xant · · Score: 5, Funny

      you're pitting a machine generating questions and answers against a machine designed to answer questions.

      You make it sound like that's hard. Here's a question that a machine could generate that another machine could not answer:

      "What number am I thinking of?"

      --
      It's rare that you're presented with a knob whose only two positions are Make History and Flee Your Glorious Destiny.
    11. Re:I don't get it by petermgreen · · Score: 2, Informative

      To detect humans, wouldn't it be easier and less costly, and perhaps even more effective, to hold a large database of questions that are readable and solvable only by humans?
      I guess the question becomes how large is large. If you reuse tests too much then the spammers will just build their own database of soloutions.

      Using a database of non computer created challenges is a good idea but there needs to be a system for keeping that database topped up. Recapatcha for example picks out words from old books that thier OCR software fails on and uses them to test your users.

      Normally they give the user two words, one for which they know the answer already (that is at least two people have given the same answer for it) and one they don't. but if they see failures from an IP they switch to giving the user two words that they know the answer for already.

      --
      note: i'm known as plugwash most places but i screwd up registering that here somehow in the past and now can't register
    12. Re:I don't get it by VeNoM0619 · · Score: 3, Interesting

      Asirra asks users to correctly classify images of either cats or dogs using a database of three million images provided by animal-rescue organizations.

      Only cats and dogs. Like I said earlier, don't limit it to just a few species. Pick one at random.

      Example: You are shown 20 pictures, all of random animals, it asks which one is the cutest aardvark, then which is the happiest turtle. Continuing random traits with random animals. Their flaw was limiting it to just dogs and cats.

      Or to take it to a different level. Most attractive/sexy/cute/old/etc. female(or male). Computers cannot tell what is the "most" prevalent "society" based trait of a picture. Yes, there's programs that make peoples photos "more attractive" but that tends to fail half the time, not to mention, it doesn't compare 12 other people.

      The TFA program only knows, "given x what is a y". And that had a 50% chance to guess between cat/dog. Not: given a-x, rank y in order from best to worse.

      --
      Disclaimer: I am not god.
      We may not be created equal
      But we can be treated equal.
    13. Re:I don't get it by grumbel · · Score: 2, Interesting

      The problem is that you cannot generate pictures of kittens automatically.

      Of course you can, thats what we have 3d graphics for. The nice thing about 3d graphics is that you can randomly vary the pose, texture, background, camera angle and so on, so you can produce a pretty much infinite amount of 2d cat pictures. The nice thing about this is that the spammer only gets to see the final 2d render, not the 3d data used to generate it, that way you can easily generate the pictures, but the spammer will have a very hard time getting information out of them. And if cats aren't enough, you can throw a heapload of other 3d meshes into the mix. You can even make this extra hard in that you not only have to click on the picture with the cat, but the cat itself. The server knows where the cat is in the 2d picture, since he has the 3d data, the client on the other side has no easy way to figure that out, which makes brute forcing quite a bit harder. You can also have many variants of questions, like "click on the two cats that look the same" or "click on the cat that has the same texture like the carpet on which the dog lies" or whatever. And you can of course also throw the spammer off by having picture of the cat inside the scene where the cat itself is.

    14. Re:I don't get it by kellyb9 · · Score: 3, Funny

      Asking simple math or site-relevant questions are not only easier for humans (I'm talking about "What's 5 - 3") to read, but they're harder for automated parsing by software to crack.

      If you really wanted to screw with these bots, you would've made the question 4 divided by 0. :-)

  4. How about by Rik+Sweeney · · Score: 5, Interesting

    Instead of asking someone to type in the letters, numbers or how many cats there are in the photo, just randomly generate some scenario:

    "Jim and Sue go to the park on Sunday. Billy the dog goes too."

    Then you can ask random questions like:

    "What is the name of the dog?"
    "What day did they go to the park?"
    "Where did they go?"

    That might work OK for a while...

    --
    Summation 2
    1. Re:How about by pla · · Score: 3, Insightful

      Instead of asking someone to type in the letters, numbers or how many cats there are in the photo, just randomly generate some scenario:

      That would work wonderfully, if you could truly randomize it (by which I don't mean anything so stringent as neutron sources or the like), rather than using a library of question templates.

      The problem, though, you need a better quality of AI to generate arbitrary easy-but-obscure questions as you do to solve them... Keep in mind you need questions that anyone with a 3rd-grade education could read and solve, which limits you to simple grammar, small words, concrete ideas, and no math harder than addition, subtraction, and inequality. Modern AI can already parse and solve those problems fairly well.

      So, you end up using a library of question templates, and once an attacker has seen enough of them, he can reliably fill in the blanks and arrive at a deterministic answer, no massive CPU power or cool AI required.

    2. Re:How about by Hatta · · Score: 4, Insightful

      Keep in mind you need questions that anyone with a 3rd-grade education could read and solve

      Why? Personally, I'd prefer to participate in forums that require a college level education to participate in.

      --
      Give me Classic Slashdot or give me death!
    3. Re:How about by sunking2 · · Score: 3, Insightful

      Oh please, a parser from a 1985 adventure game could figure this out :). You have a few nouns and a few verbs and adjectives. How many questions could you possibly ask from the first sentence? probably less than a dozen. At worst you have like a 1:6 or so chance of picking the right noun to try. If asked to do it this is probably one of the simpler things to accomplish. Creating a parser that can read at a 2nd grade level isn't all that hard.

    4. Re:How about by Tanktalus · · Score: 3, Funny

      And you're participating in slashdot because...?

      (Oh, I suppose that there probably is no such forum...)

  5. when... by cosmocain · · Score: 4, Insightful

    ...will we learn that, if there's a fundamental flaw in a protocol, there's no way we can prevent it from being abused. every measure will sooner or later have its counterpart and fail.

  6. Not a security feature by lb746 · · Score: 4, Interesting

    CAPTCHA is not a security feature. It's a way to help avoid robots pretending to be humans. Anyone using it as a security feature is just giving more reasons for people to find ways to break them.

    All in all, it's time to get rid of CAPTCHA and move on to some more logical system that would be more difficult, such as a system where users are asked to answer a simple question that contains the answer, such as:

    If you were born in 1973 and JFK was shot in 1961, were you alive when he was shot?

    How many liters of water fit into a five-liter bottle?

    1. Re:Not a security feature by Chris+Mattern · · Score: 3, Insightful

      Of course CAPTCHAs are a security feature. Unless you have some irrational hatred of robots that inspires you to bar them from your websites, you're trying to keep them out for security reasons.

    2. Re:Not a security feature by Abstrackt · · Score: 5, Insightful

      CAPTCHA is not a security feature. It's a way to help avoid robots pretending to be humans. Anyone using it as a security feature is just giving more reasons for people to find ways to break them. All in all, it's time to get rid of CAPTCHA and move on to some more logical system that would be more difficult, such as a system where users are asked to answer a simple question that contains the answer, such as: If you were born in 1973 and JFK was shot in 1961, were you alive when he was shot? How many liters of water fit into a five-liter bottle?

      It sounds like a great idea, but I've met plenty of people who wouldn't be able to answer either of your questions. To steal a random quote from the internet:

      "Back in the 1980s, Yosemite National Park was having a serious problem with bears: They would wander into campgrounds and break into the garbage bins. This put both bears and people at risk. So the Park Service started installing armored garbage cans that were tricky to open -- you had to swing a latch, align two bits of handle, that sort of thing. But it turns out it's actually quite tricky to get the design of these cans just right. Make it too complex and people can't get them open to put away their garbage in the first place. Said one park ranger, "There is considerable overlap between the intelligence of the smartest bears and the dumbest tourists."

      --
      They say a little knowledge is a dangerous thing, but it's not one half so bad as a lot of ignorance. - Terry Pratchett
    3. Re:Not a security feature by camperdave · · Score: 2, Insightful

      How many liters of water fit into a five-liter bottle?

      Hmm... That depends. How much water is in the five liter bottle to start with?
      Is there anything else in the bottle?
      Does it have to be a whole number of litres?

      Assuming an empty bottle, and integral numbers of litres, the following can fit: 0, 1, 2, 3, 4, and 5.

      --
      When our name is on the back of your car, we're behind you all the way!
    4. Re:Not a security feature by Anonymous Coward · · Score: 5, Funny

      > If you were born in 1973 and JFK was shot in 1961, were you alive when he was shot?

      I have developed a device that answers random yes/no questions correctly 50% of the time. Me and my flip-a-coin-bot will take over the world!

    5. Re:Not a security feature by spyrral · · Score: 2, Insightful

      How many of these questions would you have? Suppose you spent the time to make 1000 or 10,000. The attacker would simply have them solved by a group of humans (say using Amazon's Mechanical Turk) and put the question/answer pairs into a dictionary for automated attacks.

    6. Re:Not a security feature by corsec67 · · Score: 2, Interesting

      If you were born in 1973 and JFK was shot in 1961, were you alive when he was shot?

      How many liters of water fit into a five-liter bottle?

      That is also a CAPTCHA, "Completely Automated Public Turing test to tell Computers and Humans Apart." A CAPTCHA doesn't have to be text in an image, that is just an easy test to auto-generate.

      And, it fails the "solve problems for porn" test. The problem is spammers using real people to do stuff en-masse, so any kind of CAPTCHA wouldn't prevent that.

      --
      If I have nothing to hide, don't search me
    7. Re:Not a security feature by Tablizer · · Score: 3, Insightful

      [bear-proof trashcan] Said one park ranger, "There is considerable overlap between the intelligence of the smartest bears and the dumbest tourists."

      To be fair, the bears have more time to figure out the can. A tourist will just toss the trash on the ground if it takes more than a minute to open the can. The bear, on the other hand, may spend hours if it smells something good.

      --
      Table-ized A.I.
    8. Re:Not a security feature by Anonymous Coward · · Score: 5, Funny

      Well, I think we have a capcha to prove someone is a lawyer.

    9. Re:Not a security feature by Anonymous Coward · · Score: 2, Insightful

      If you have three apples and you take one apple away, how many apples do you have?

      Correct answer: 1 (The apple you have. The one you took away and therefore 'have')

      Correct answer: 2 (The remaining apples viewing the operation as a mathematical subtraction - expected answer from a child)

      Correct answer: 3 (You have three apples. Movement does not imply a change of ownership)

      Correct answer: 4 (More tenuous, but no assumption should be made that 'one apple' came from the initial set of 'three apples')

    10. Re:Not a security feature by DriedClexler · · Score: 3, Funny

      And if the web site is a discussion forum, you're exactly what they're trying to keep out.

      --
      Information theory is life. The rest is just the KL divergence.
    11. Re:Not a security feature by Free+the+Cowards · · Score: 2, Informative

      Wrong. Most sites with CAPTCHAs are trying to keep out automated systems because they are abusive. But this is not "security" any more than banning abusive human posters is "security".

      --
      If you mod me Overrated, you are admitting that you have no penis.
    12. Re:Not a security feature by Free+the+Cowards · · Score: 2, Insightful

      In the computer world, I always consider "security" to be a matter of allowing authorized people in and keeping unauthorized people out. CAPTCHAs are more a case of determining whether a particular user is desirable or not, not a case of authorization.

      --
      If you mod me Overrated, you are admitting that you have no penis.
  7. Ofcourse it's possible:But is it doable by humans? by anomnomnomymous · · Score: 3, Interesting

    "...says it is usually possible to make a CAPTCHA more difficult to break by making a few simple changes."

    Yes, it's possible: But keep in mind that you also have to serve the USER. When the captcha is getting so hard I can't even decipher it anymore (let alone someone with a visual handicap), it's of no use.

    I stopped using Rapidshare because of its ultra annoying 'mark the cats'-captcha: I found it near-impossible to get that right (though the other day I noticed changed that back to ordinary letters).

    --
    When you shoot a mime, do you use a silencer?
  8. Get the questions from the users by John+Hasler · · Score: 3, Interesting

    How about asking every nth person successfully logging in to generate a question? Apply a lameness filter and then perhaps ask another randomly chosen user to verify that the question is reasonable. Reject duplicates and questions that too many people can't answer.

    --
    Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
  9. Comment removed by account_deleted · · Score: 4, Insightful

    Comment removed based on user account deletion

  10. But, spammers ARE humans! by Wyck · · Score: 4, Interesting

    Well, it seems to me that spammers ARE humans. So trying to detect if the creator of the account is human or not doesn't separate the spammers from the non-spammers.

    Think about it: the authenticating machines are designed by humans, and the perpetrating machines are also designed by humans, and the legitimate users are humans too.

    Perhaps the problem itself needs to be restated: Allow accounts to legitimate users, deny accounts to spammers. Whether or not there is a human involved on either end seems irrelevant.

    - Wyck

  11. What do you mean...? by dirtsurfer · · Score: 4, Funny

    African or European water?

  12. Re:CAPTCHAs kick-start Singularity OR,,, by lord_sarpedon · · Score: 3, Funny

    Ah. So you appreciate Cameron for her intelligence huh?

    Me too. Exactly.

    (Model T-6969 I think right?)

    --
    "Strangers have the best candy" -Me
  13. No, the future is in biometrics by Chicken_Kickers · · Score: 2, Funny

    as in, make it a law that all computers sold from now on must have a genetic sequencer attached to it. Any time you want to open your email, the server will show you a, uh, suggestive jpeg and you, uh, express your, um, genetic material, into the genetic sequencer. Its totally fool proof and pleasurable as well, even if you have someone pointing a gun to your head. Crap...I just realised this won't work for women. Back to the drawing board.

  14. use humans to check for humans by markjhood2003 · · Score: 2, Insightful

    Seems the spammers are hiring boat loads of people to train their CAPTCHA-breaking software. Google and the like could do the same and hire call centers to screen applications for an email account. You want a gmail account, call a 1-800 number that connects you to some vast call center in India.