For anyone working with sight-resight, mark-recapture or photo-id in general, this tool can help with matching animals while in the field.
Side by side view allows you to do regular photo-id, while comparing two images next to each other. Standard swipe and zoom motions makes it quick and easy to compare the images.
Gallery view allows you to use the full screen to look through your catalogue and identify animals in the field.
Overlay view allows you to take two images, and put them on top of each other. A simple slider allows you to change opacity of the images, and zooming and moving the images with your fingers is a snap.