how do you add a picture at the end of your signature?

It's called smilies
here's a link to see the smilies: http://www.lissaexplains.com/forum//misc.php?s=&action=showsmilies

you can't :(

at the bottom of each page there's a little light colored box that lists the things that are enabled and the things that are disabled, and images are disabled.

but as cute_angel said, you can use smilies.