I've used Duplicate Cleaner in past and it has nice features to find and remove duplicate files. https://www.digitalvolcano.co.uk/duplicatecleaner.html
I don't often have the need to find duplicate photos anymore; but when I did I found this program to suit my needs. I believe it is a free program "Awesome Duplicate Photo Finder". Anyway you might want to take a look at it. Sorry I just read your post and somehow I missed you not wanting to delete duplicates. I believe in this program it would require manual deleting. Again sorry!