I’m trying to create a single directory with photos and videos on four different hard drives, some are renamed duplicates. Is there freeware that can create a hash so I know if I’ve got a duplicate?
There are various freeware programs for detecting duplicate files. Here are two articles listing some programs for Windows, many free. If you’re not using Windows, try googling “find duplicate files” plus the name of your OS.
Well yea I have heard of this thing called google, I was hoping to tap into the collective experience here 
I know that I’ve spent many an hour trying out freeware program after program, with one or two I’d actually want to use in the end.
Some time ago I used HashMyFiles to try to find some misplaced files at work. Didn’t work as they had been archived off but the utility was easy to use. I note at the link they have another program SearchMyFiles with a Duplicate Search Mode.
ETA I should mention Gizmo’s Freeware which I use all the time for stuff. Everything is reviewed by someone who is a genuine user.