Duplicate photos, comparing two folder, why is it so hard?

First of all I have a brain injury, but still I'm not sure why I'm doing this so hard.

I have 2 folders, one gather from photos on my computer. And the other are all of the facebook photos. I have made it so the folder are just photos, so subfolders. So I just want to see if my computer folders are in the facebook photos. I've tried using DupeGuru and Duplicate Photos fixer and I just can't get it to compare the two folders. It seems to always give duplicates within folders and not across folders :(

Can anyone suggest a simple way to do this? I don't care if I need to buy software. it just needs to be simple. Thank you for any help :)