Identifying Manipulated Images

Jamie found a cool story at MIT Tech Review. (As an aside, it sits behind an interstitial ad AND on 2 pages: normally I reject websites that do that, but it's a slow news day, so I'm letting it through.) Essentially, software is used to analyze light patterns in still photographs. Once you can figure out where the light sources are, it becomes a lot easier to determine if an image has been photoshopped.

Comments

Detector == Quality Control

[Anonymous Coward]

People who manipulate images will use these tools for quality control: When the fabrication passes all tests, it is ready to be released.

Colombo did this on his 1970's TV show

[jimwelch]

Someone wore a photo mask and tripped a speed camera to give their partner proof that they were across town (LA) at the time of the murder. He noticed the shadow under the nose was wrong by comparing previous and following pictures from the same camera.
I am not sure which episode it was. Peter Falk as Det. Lt. Colombo

Finding Photoshopped Pics for Fun

[Dan East]

Does anyone else have a habit at looking at pictures and trying to see how they've been manipulated? These types of pictures are rampant in advertising. Pick up any magazine and start looking, and the poorly edited pictures will jump out quickly. The more professionally edited pictures have much more subtle problems, and can take a bit of poring over to find. Many product images (on packaging and in catalogs) are the same way, and are usually the worst edited of the bunch. Some things I look for:

• An object rubber-stamped in multiple places. Each copy is identical, which gives it away. They are often scaled, rotated or mirrored to make them look more unique.
  
• Lighting and shadows, which is what the algorithm in this story deals with specifically.
  
• Focus. Often multiple objects will be in focus at varying distances impossible with a single shot.
  
• The same image of a person is used in multiple shots. This is most prevalent in product images in catalogs.
  
• Poor masking, where edges of objects are over or under processed, either clipping part of the object (hair can be particularly tough to do), or showing some color edges from the original background.
  

Anyway, that's just the geek in me I guess, because I really do enjoy finding flaws in images. What I hate is an image that has a sort of surreal perfection to it that I know must be composited, but I can't find any smoking gun.