Finding duplicates

[TimeTraveler7]

Is there any way to find duplicate photos on iPhone/iPad? For example, if you use an app to download wallpapers, chances are that in time you end up with some duplicates (of pictures you liked but forgot you had already downloaded them earlier); how do you detect and get rid of those (other than manually checking the photos)?
Usually not a problem on a computer (if the filename is the same, you get prompted about overwrite/cancel etc.), though.