That is a fake application. It's been around for a while on Treo's and Palms etc.
The finger print isnt yours....it's a "novelty" security thing. Basically you pretend like you need to scan your finger print to unlock your phone....and when you show it to people and have them try it, they can't get in when they scan their finger...then you show them how YOU can get in when you scan yours - and its' because there's an additional button that needs to be pressed as you do the fake scan. I assume for iPhone, you hold the home button when you do the scan and every time it will unlock it with that combination no matter who does it. But the print that shows up is the same every time, just a picture of a finger print. It will show up wherever you press but that's about it. Totally fake.
iPhone is not capable of actually getting a finger print scan from touching the screen. That's way more intense than it seems....it's not sensitive enough to know where the exact ridges are.