What can be improved:

• cache progress for images and videos somehow (but that itself would only be reliable with hashing - are file timestamps on android reliable?)
• implement backup
• increase support for older android versions (or at least notify user)
• add support for additional methods of comparison of images (this would increase scope by a lot)

Feel free to fork and call it your own. I use the tool for my own media - there is no warranty for this software. Make a back-up manually before you run it.