The thing is that only the avatar (the image below your user name) can be uploaded from your computer. And it has to be suuuuper smaaalll!.
You CAN add a photo to your signature. It HAS to be linked from another web site, not from your pc. You can actually upload tons of photos in websites like www.photobucket.com
. Once your photos are on a web site, they can be easily linked to your signature or even your message.
That'* how we people here have great illustration of messages and sigs with images.
You can also go to "Your Ride" forum and look at "Tips for Photos" thread for more info.