You post pictures by wraping the URL of the image in the bbcode for and image.
One of my Avatars' URL is: http://blog.pnc1.com//images/blog_pnc1_com/carsinigin/4/o_avatar31624_1.gif
if I want that to show up as a picture I wrap it with [ img ]http://blog.pnc1.com//images/blog_pnc1_com/carsinigin/4/o_avatar31624_1.gif[/ img](without spaces) like so;
You will need to find some webserver to host your image on.