The application is extremely easy to use. Upon first launch, the user is being walked through the fingerprint scanning ordeal. One can choose which digit to scan (any of your left or right hand's five fingers), and then it becomes a question of placing said digit in front of the rear camera and snapping a bunch of macro photos. The app then extracts actual fingerprint readings from these images, learns them, and becomes impressively consistent at recognizing finger patterns from them.
Most surprisingly, the app works well enough, although the practicality of this fingerprint unlocking method is unquestionably low, and the issue of protecting those hi-res fingerprint images stored on your device hasn't been elaborated upon by the developer. Thus, we'd like to think of the application as more of a proof of concept, rather than an actual fingerprint unlock solution. However, FPAU does support passcode and pattern unlock methods, so it can double as a perfectly fine app locker while pulling off its fingerprint scanning shtick.