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How To Check JPEGs for Photoshopped Modifications

By Sam Cook

A new online tool does a quick error level analysis of images, highlighting sections that may have been altered.

Ever wondered if a digital photo has been manipulated? Sometimes it’s all too ( hilariously) clear when an image has been altered, but when crafty photoshoppers have been at work, it’s hard to be sure what’s real. But now thanks to a handy online tool, anyone can perform a quick forensic check of a JPEG picture and easily see which sections might be fake.

error level analysis (ELA), which checks quality level across the image and highlights sections that seem to be off from the rest of it. Here’s how this ELA utility separates truth from fiction.
 
  As you may know, JPEG images go through a compression algorithm each time they are saved, creating a certain amount of quality loss. If you save a JPEG a few times and then copy in an element from another image, the added bit will likely be at a different quality level than the rest of the picture—the new stuff has only been compressed once, while the rest has been compressed several times.


The online tool shows different image degradation levels using brightness, creating a clear visual separation between areas of different quality. Brighter elements have been altered more recently, while darker areas have been saved, and compressed, many times. ELA isn’t perfect—it will have a hard time finding edits if the whole picture has been re-saved repeatedly, is at a very low JPEG quality, or if all the source images are equally degraded. But for high-quality JPEGs this tool is gives you a good idea which sections of the photo you should examine more closely.

You can read more about ELA over at the The Hacker Factor Blog.