Challenge
| Subject: | The Case of the Deadly Disk | ↰ |
| Difficulty: | ●○○○○ | |
| Duration: | 4 minutes (estimated) | |
Shortly after Kim Jong Un became North Korea's new leader, a picture was distributed of him holding an object. This image quickly became an Internet meme as people digitally altered the photo. Here are several pictures of Kim Jong Un holding objects. However, none of these are original photos. At minimum, each has been cropped, resized, and resaved from some unknown original photo. With all but one of these pictures, there has also been one or more digital alterations beyond cropping, resizing, and resaving. Floppy Disk Winning Card ID Card Gangnam Style Click on each picture to view the analysis page. Using Error Level Analysis (ELA), can you identify which of these pictures are digitally altered? Based on these pictures, what was the original object that he was likely holding? JPEG is a lossy file format. Each resaves causes the picture to degrade.
ELA shows the JPEG compression level's error potential. Each time the
image is saved, it degrades and gets a little darker under ELA. When a
portion of a picture is digitally altered, the modified area appears
brighter under ELA. Digital alterations appear as an inconsistency. If there is an areas that is extremely bright or extremely dark when compared to the rest of the picture, then it likely indicates a modification. Modifications, such as scaling a picture smaller, causes every pixel value to change. (The scaled color becomes an average of its neighboring pixels.) If a picture is scaled smaller, then its edges should appear bright under ELA, but solid surfaces (like his black jacket or the background colors) should remain dark. Kim Jong Un was originally holding an ID card. The floppy disk and playing card both have ELA results that are significantly brighter than the rest of the picture. These items denote modifications; they were digitally added. With the ID card, all edges have similar ELA intensities and all surfaces are similar. While the picture has been resaved (darker ELA), the entire picture is consistent. (If it was modified, then we cannot detect the modification.) The gangnam picture was dramatically altered by being resized. Every pixel changed due to the scaling, so everything is bright. However, the CD case in his hand is still brighter than anything else, so it was added last. ELA does not identify the headphones as being different from anything else due to the scaling. | ||