A fair concept, but it's a problem that even the creators find it necessary to use text to tell users that they have to click on the images to use them.
It implies a UI problem they haven't figured out - and it's one of the reasons I wouldn't use it.
Instead of a click, why not make it a roll over?
That would probably be a great improvement. It'd still need something to signify that you interact with it by hovering.