I had exactly the same problem, and well over 150,000 assorted photos, many of which had the same names or numbers, coursed by early cameras which reset themselves, when you changed the batteries
There does appear to be a complete answer to this problem,
It s a small little known program called VisiPics, (it was apparently written by a chap who couldn't find an answer to his own photo problems)
However like most other things, the instructions are a bit vague, so the following may help !!
This program will handle all your photo files at one GO, even if they are located on a stack of large hard drives, (if some of your photos are on CDs, then I would suggest you copy them to hard drives first), Personally I would not use this program on the whole of C:\ drive, (only on the directories)
When you first open this program, I suggest you go to the (Tools) menu and un-tick the item that says (loosen filter automatically), then go to the (Filter) Tab, and slide it up to Strict
If you'd like to see how the actual program works ? , choose a few individual directories, which you know have duplicate file names in them, click the upper curved button to lock them in to the blank window, and then click the green button to start, and watch the information in the center of the screen
This program appears to pick out identical photo information, irrespective of file names, sizes or anything else, please give yourself time to get used to the program, which is FREE, with the proviso that if you like it, you may make a donation
The only problem you may come across, is that if you use the (Auto-select) facility, which I nearly always do, you will find that some of the individual photos are not always in the directories you expect, this hasn't been a problem for myself, as I can then sort them where I like, knowing there are absolutely no duplicates, one small last item, if your not happy with the settings you have chosen or it's taking too long, just shut the program down, it does not appear to damage any files ?