Bounce at screen

http://www.ontheground.be/

i’ve seen plenty of sites do this effect…but how is it done… when a image comes form the back and bounces directly at the screen

(when on the site (http://www.ontheground.be/) click on portfolio and then one of the buttons to your left you will see what i mean)

if someone can point me in the direction to how that’s done i would appreciate it…