Spotlight: Micopi for Android generates unique, abstract contact pictures from the entries in your address book
There are two approaches to using Micopi. The first one is about selecting each contact individually and letting Micopi generate a pack of abstract images. You can freely choose between them and save the one you like as the unique contact picture for the desired entry. The other is called "Automatic Mode" and it allows you to either overwrite all contact images with uniquely generated ones, or only work its magic on contacts that have no pictures.
However, before you go trigger-happy on Micopi, do mind that applying an image to a contact entry can't be undone, and neither can other changes made by the application. Thus, the developers recommend a backup of your contacts and related pictures, just in case any incidents happen. Micopi is a free download from the Google Play store.