This is a freeware pgm that lets you compare file sizes, names and content. But it does not give you a visual check by opening a picture file.
"Duplicate File Finder 184.108.40.206
This file comparison program supports unlimited number of files, folders or drives. Drag and drop folders or shortcuts that you want to scan. You can load and save different search profiles, and the last used search profile is automatically saved on exit. The fast search algorithm offers various search options, and you can export duplicate file list information to various file formats."
Hope that helps a bit.