Is there a way to find duplicate images in Ubuntu?

diff will help you find duplicate files in two different directories, but if your mess is greater or if, for any other reason, you want to find duplicate (exact) image files in a whole directory, including subdirectories, you can use the gthumb image browser viewer, which is probably already installed in your system.

Gthumb provides a tool to search for duplicate media/audio/video/images/text/all files in a directory. To do this, just select your directory in the view mode that displays a left pane with your directory tree, and then, from the menu select Edit>Find duplicates... a dialogue window shows the duplicates and lets you choose which file(s) to delete. This procedure is visual and helpful in many cases; but it is slow, if you have too many duplicate files to delete.

just use diff directory1 directory2

If you want to find duplicate files, you can use fdupes program as explained in this question: How to find (and delete) duplicate files

However, with a photo collection this won't find different versions of an image (you can have multiple copies of an image with different metadata, different resolution etc.)

To find dupolicated images you can use DigiKam, which is in general an awesome tool for managing a photo collection. It has Find Duplicate Images Tool: