Anki Doodle

Anki is a poplular flashcard platform. There's a plugin called "Image Occlusion Enhanced" for the desktop version of Anki that helps you make image occlusion cards(use geometry shapes to hide part of an image on the front side of flashcard).

Now, with Anki Doodle, you can do this right on your Android device, in a simple and elegant way. You can even take a picture your textbook and make a dozens of occlusion cards in a minute!

Note: to use Anki Doodle, ensure that you have Ankidroid installed.