It just likes what you did by running the app and hold the stand-by button then push on the home button.

When you run this code, it will capture the current screenshot and add into the Camera Roll.

It’s not yet included in the official SDK but you can get it run easily.

@interface UIApplication (Extended)
-(void) _writeApplicationSnapshot;
@end
[[UIApplication sharedApplication] _writeApplicationSnapshot];

Yo!