Anyone who has a hard disk clogged with photos will welcome Visual Similarity Duplicate Image Finder ($25, free demo). This utility does an excellent job of hunting down not just file duplicates, but photos that are so similar that you might as well erase some of them to get back hard disk space. It's exceptionally easy to use, exceptionally fast, and does an exceptionally good job at fulfilling its promise.
Tell Visual Similarity Duplicate Image Finder what folders to check for duplicates and similar files, and it quickly goes about its work. Rather than just check for file names, it actually examines the contents of each file, and looks for duplicates and similar files that way. It even compares files of different types, for example, a .jpg file and a .gif file, to see if the files are similar to one another. It handles every popular graphic file format, including .jpg, .gif, .tif, .png, .bmp, .pcx, .wmf, .emf, .ico, and others. VSDIF goes about its work extremely quickly; it took only a few minutes to compare hundreds of graphics files on my PC.
After it does its work, Visual Similarity Duplicate Image Finder shows you all images it thinks are duplicates or very similar. It rates their similarity and lets you visually compare them. You can then delete any that you no longer want. Note that this is a demo version, so that it won't delete any files unless you register.
Author MindGems also offers Fast Duplicate File Finder, a free program that performs a similar task, But Fast Duplicate File Finder doesn't have the same sophisticated tools for finding similar images, and only finds exact duplicates. If you want to find duplicates only, you probably can get by with the free Fast Duplicate File Finder. But if you want a sophisticated way to clean out similar photos, Visual Similarity Duplicate Image Finder may well be worth buying.