My bank website does this, however, it simply has a list of predefined images. It presented me a random image from that list when I created my account. It also allowed me to pick (change) the image to one of my liking by presenting me 8 different images. There are obviously more than 8 images in the library as each time I go to change my security image, the 8 images I get to choose from are different.
Also, it forced me to create a security phrase. It displays both the image and the phrase on the page where I enter my password.
Doesn't seem too complicated. 9999 images would get you the same security as a standard 4 digit PIN.