Earlier today, I took some pictures of my niece, edited them and then wanted to print them. But before I could print them, I had an errand to run. When I came back, I had no idea which of the pictures I had edited before and which was the original one. You can check the file modified dates, but my picture editor saves the pictures using the same modification date. The FC command in Windows is useful, but it does not tell you the exact location of changes (in terms of pixels). After looking up for 30 minutes, finally I found out DiffImg which is an open source application that can find out the differences between two images and highlights detected differences visually in an intuitive GUI interface.
You can get the DiffImg program from its sourceForge webpage. The download is available in form of a setup installer for both the 32-bit and 64-bit editions of Windows. After the installation, it can be launched from its desktop shortcut. Strangely, when I tried to launch the 64-bit version of DiffImg on Windows 8 Pro 64-bit, it failed to run. So I had to download and run the 32-bit version of DiffImg.
As soon as you launch DiffImg, it asks you for selecting two pictures to compare. It can open almost all types of image formats including the popular ones like JPEG, GIF, BMP, PNG, TIFF and more. One of the images is called the base image and the second image is for comparing it with. The base image is indicated with a yellow smiley icon, while the image-to-compare is shown with a green martian/alien icon.
You can click on the unusually large Original, Modified and Difference icons the left-side sidebar to see the respective pictures in the center. The icons for the functions are also present in the DiffImg toolbar. The difference is shown at the pixel level. The red pixels indicate small change (possible due to saving same image in different editor or using some lossy compression), while the yellow pixels indicate large change (mainly because it was edited or something else was drawn in that area).
If you understand the histogram for the picture, then it displays the histogram for the both of the opened images as well as the different pixels. In the histogram, you can easily see the pixels of which tonal values are different in the opened images.
Conclusion: The DiffImg program provides you with an easy way to find out the difference between two images and shows you which pixels are different between two identical looking images. Although DiffImg does not come with any documentation, it does not really need one – you can learn it use quickly without much problem.
You can download DiffImg from http://thehive.xbee.net.