let's just say:
sometimes a mistake can be used to create something new.
if the image is as big as the space for it it can be tapped,
if it is smaller it can be slided to the right,
IF IT IS BIGGER IT WILL MOVE TO THE LEFT AND ALSO EXCEPT THAT
COMMAND (you can slide left or right)
the screen is unlocked when the right end of the slider hits the right end of the space in the background. If the image goes beyond that point it has to be slided back to unlock the screen. It's not too special actually.
Just try it. It's pretty easy. Getting the images to the right position is the tricky part, but it only took me a few minutes to do the fingerprint and the first one with the reverse direction.