I looked for some free software on the net and discovered Easy Duplicates Finder:
http://www.easyduplicatefinder.com
On a directory containing 20.000+ files, the program took about 2 minutes to find all the duplicates (pictures & videos). Saved me a ton of work. And it's free! Great little tool.
Of course, the program will only discover exact duplicates. If you have the same picture in different sizes (one 600x900; one 1200x1800), the tool will not recognize them as doubles. The same goes if the logo has been changed, if the picture has been Photoshopped...
Duplicate Photo Finder is specifically designed to find similar images, taking resizing, color corrections... into account.
http://www.easyduplicatefinder.com/duplicate-photo-finder.html
Just downloaded the tool and started using it. It works a treat!
But it's only a trial version. It will find the duplicates for you, but you need to buy a licence to actually delete the doubles. Of course, finding the doubles is the hard work. Deleting them can easily be done manually. I have to add that I am in no way associated with Easy Duplicate/Photo Finder. I just found them to be very handy tools that may be of interest to other EBI members. If anyone has experience with similar tools, please let me know.
Loso