I've just published Disk Health on Mac App Store: It manages safely iTunes, Photos and iPhoto libraries to preserve the integrity of the library itself.
It's a disk cleaner and duplicates finder with lot of features like old files and big files detection, parametric search allowing you to choose file size, file date and combination of both, fast duplicate detection algorithm with advanced 512 bit hash to avoid false positives.
There is a lot of app for Mac OS and for iOS search "duplicate photo finder" on the App Store for device you need. If you need to find duplicate photos and videos among Mac and iPhone (iPad) there is only one app I know.
it's called interPhotos. You need to download it for iOS and Mac and scan both devices for photo copies.
The app is free. it offers in-app purchase for video searching, but photo scan and delete is completely free.