Every image on every page is replaced with one of your choice!
You can use this to prank people.
Get five minutes with their computer.
Install Greasemonkey and this script
Choose an image and watch them go crazy saying they got a virus and computer has been haxored.
You could go even further and find a way to hide the greasemonkey button
Current image is a greasemonkey logo
Any problems please start a discussion, I don't keep these up to date unless someone tells me to.