changing images/pictures

hellu. i have a slight problem i hope someone can help me with. A place where i chat uses pictures to represent your online presence, and sometimes, people use porno pics. well, theres only so much i can take of that. What id like to do is change the persons picture to a blank or blacked out pic. i know how to change text in other programs but im having a time trying to chage pictures. Any help would be appreciated.

http://element.virtualave.net