Easy Duplicate Finder from WebMinds is a useful tool for macOS 10.6 or higher to find and remove duplicate photos, documents, MP3s, videos, and more on your Mac's hard drive. It can help free lots of hard disk space and is super-easy to use.
To use, you just drag and drop folders into the program window and start the scan. Easy Duplicate Finder will do the rest. There are flexible file scan settings, a live preview, and an Undo button. However, there are other apps that do the same thing at less cost.
Easy Duplicate Finder costs US$39.95. CleanMyMac is also $39.95, MacBooster, also $39.95, and Mac Washington Machine, $29.99, are priced the same (or less). They also eliminate duplicate files, but perform other hard drive maintenance tasks, as well. You can buy Duplicate Detective, Duplicate File Cleaner, or Duplicate File Detector at the Mac App Store for, respectively, $3.99, $9.99, and $1.99. All do a decent job of finding and eliminating file duplicates.
However Easy Duplicate Finder was recently revved to version 4.7, which makes a good argument for the application as the best duplicate finder for the Mac. Its new scanning mode lets you scan your iTunes libraries for duplicate songs and delete the duplicates in a single click without having to worry about any synchronization issues. It also allows you to delete the duplicates without having to inspect countless folders that contain your music.
Another advantage of Easy Duplicate Finder’s iTunes Scan is that the program synchronizes iTunes and Photos after it deletes duplicate files. The synchronization is automatic. I don't know of any other file duplicate deletion app that tackles these tasks.
You should check out all these apps and see which ones best serve your needs. If your needs are very simple or very complex, there are other alternatives on both ends of the needs spectrum.