PicaDup is specialized in research of sufficiently similar images to be considered as duplicates. The useless images can then be deleted to save space on your device and/or SD card.
This application can delete photos on the SD Card for the Android Lollipop version and above.
Select one or more directories on your mobile and PicaDup will search for you all the pictures with the same views or subjects. Once the analysis is complete, it is possible to delete images in each group found.
This completely free application has no restrictions.
PicaDup incorporates advanced algorithms and features from the Panaustick application from the same author (http://en.panaustik.com). Hence it does not give false positives. It can handle a large number of images quickly. It detects duplicates even if the images are not the same size, have a different orientation or exposure, or are more or less sharp...
At the first run, images are scanned and analyzes are saved which can take some time. Then next runs are much faster.
If you are looking for less specific application, searching for exact duplicates of files of any kind, you can try FileDup (https://play.google.com/store/apps/details?id=com.panaustik.filedup) which searching for exact duplicates is therefore much faster.