From Elvanör's Technical Wiki
Finding image duplicates in collections
- The best tool by far is Digikam, it is very convenient to quickly find duplicates and erase them. You should usually select a similarity factor of 65-70%.
- The main default of Digikam is that it cannot work on folders that are not part of its "collections" (although it is quite easy to add a folder to a collection). Also it seems to create a hidden (starting with a dot) folder in some directories, to implement trashes.
- A tool that can work as well is Geeqie (in Portage). However I found out its behavior to be a bit strange and thus Digikam is better (also, it's not possible to view easily found duplicates to confirm them, which is very problematic, and Digikam does that very well).
- Choose the folder where you want to search for duplicates (you can select a top-level folder and scan recursively), then choose Compare by Similarity (or Similarity - High).
- Once it gives you a list of found duplicates, you can select them all, choose "View in new window", then click on the new window to slideshow the images.
- The most convenient way to remove the duplicates is for me to move all found images to a new place (other folder) then open the folder in Gwenview and remove duplicates manually.
- Digikam also has some duplicate searching features (not tried yet).