You need to have an account at a website which stores photos, such as photobucket.com
After you create an account at that website, you can upload a photo. (Sorry I don't have step-by-step instructions on that, because they changed the procedure for uploading.)
After you have uploaded the photo you want to use, hover your mouse on that photo.
Some information will appear under the photo.
Under the photo, click in the IMG CODE box
If you have a Mac, you will then need to right click in the box, and click on COPY
Log onto the disboards
Click on CP to get to the Control Panel
Click on EDIT SIGNATURE
Click on the place where you want to insert the photo
EDIT
PASTE
Click on PREVIEW SIGNATURE to see if you like it
If you like it, click on SAVE CHANGES.
I had some trouble with mine because the picture has to be pretty small, and it was hard to crop it exactly the way I wanted. Some pictures might be easier to work with than others.