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HTML Encoded Captchas
rangeva writes to tell us about a twist he has developed on the common Captcha technique to discourage spam bots:
HECs encode the Captcha image into HTML, thus presenting an unsolved challenge to the bots' programmers. From the writeup: "The Captcha is no longer an image and therefore not a resource they can download and process. The owner of the site can change the properties of the Captcha's HTML, making it unique,... add[ing] another layer of complication for the bot to crack." HECs are not exactly lightweight — the one on the linked page weighs in at 218K — but this GPL'd project seems like a nice advance on the state of the art.
Another useful web page trick is Javascript encoding of PGP:
http://www.hanewin.net/encrypt/
Instead of feedback forms that send plain text messages back to you for all to read, it lets you encrypt the text in the browser using PGP before it is sent. If you don't want people snooping on submitted messages this is a quick and simple way to do it.
Thunderbird has a plugin that lets you send and receive GnuPGP mails.
http://enigmail.mozdev.org/
It's not offtopic (bad moderation), it's directly related to captchas on forms and just like the trick of doing the capture in the browser this is using, its the same thing, only for encrypting the message sent.
I've used both captchas and this script in the same project and if you're using this html captcha to do forms, you'll likely do the same.
Comment was:
Another useful web page trick is Javascript encoding of PGP:
http://www.hanewin.net/encrypt/
Instead of feedback forms that send plain text messages back to you for all to read, it lets you encrypt the text in the browser using PGP before it is sent. If you don't want people snooping on submitted messages this is a quick and simple way to do it.
Thunderbird has a plugin that lets you send and receive GnuPGP mails.
http://enigmail.mozdev.org/