usually an image rotator. i have an unused one here

if you keep refreshing, the random image will be displayed

source here , if you want to try your own

one key is to get the url to pan out in the ubbt world and be treated as an image. ubbcode parser usually flags it and you don't get your image.

[Linked Image from gettyguy.com]

if you refresh my post it will change the image. just do a quick quote and you'll see the img code used.