Trying to find the best out of a series of 15 photos shot in sequence? This app shows two photos on the screen in order to compare them. Zooming and panning is synchronized, so focus and composition can easily be compared.
The best photos can be selected, and the selection eventually shared. Alternatively, all photos which were NOT selected can be deleted from the device, freeing up space while keep the best photos.

Features: long-press image to mark it as starting point for comparison. Navigate up/down through an image folder. Long-press navigation to “catch up” to image adjacent to the one in the other view pane. Select images for later processing. Synchronize zoom/pan, or disable synchronization to change views of panels independently. With selected images: share (using standard Android share mechanism, beware that more targets are available if only one image is selected), delete all the NOT selected images in the folder (this will really, physically delete the files. They’re gone afterwards. BE CAREFUL TO NOT DELETE ALL YOUR PHOTOS!)

I use the app regularly to decide which photos to post to https://www.instagram.com/simonniederberger/.

Open source at https://github.com/sniederb/photocompare