CompareDir

Did you ever copy many files to a portable usb-harddisk and use another system to update or delete files ? And later have trouble to find the few files you changed among all the others ?
CompareDir does just that: it can compare 2 directories + subdirectories and you decide what files you want to keep, copy or delete.
Manual: point it at a MasterDir, a SlaveDir than
click "Diff" = show only the files that are available in only 1 directory-tree.
Or click "All" = show all files in both directories.
Or click "Eq" = show file only the files that are the same.
Note the program cheqs FileName, FileSize, FileDate and (sub)directory. It does not compute md5 sums because that would make it extremely slow. Mind you i use this regular for directories with 2000 photos.
Based on Python, pygobject and gtk3.
+ Python-pillow if you want to compare 2 images.
No installation:
untar -xvzf CompareDir.tgz
where you want and run.