I know there's software which will search for duplicate files, but the last time I used it I found it crashed if there were too many. Bad memory management
Simplest approach is to produce a spreadsheet with two columns, one for each directory. It should be quite easy to go through them then.
Open a command prompt in each of the directories and type dir *.* /s /b /on > files.txt
That will generate text files you can import into your spreadsheet of choice. Use *.jpg or whatever instead if you want to filter.
sigh's contentedly. those were the days. 
