there are two options, ill try to avoid a long post.
first and easiest in my opinion, is the photo is already online. If this is the case use the imag tags.
FOR EXAMPLE:
{img}http://www.imagelocation.com/imagename.jpg{/img] substituting the {} with a [] respectively.
Next option is to attach the image to the forum. WHen you post a reply, you hit continue on top of the the page there is small area that says "You may attach a file if you like (no bigger than 2000000 bytes please)." then a blank box, then a browse button. If you hit the browse button, another window will pop open, from there you have to search on your pc where the image is stored. Once you find it, you click on open it and it will attach your local files location and after you hit continue again, it will upload for you.
ninja edit, Jake beat me to it.
![[Linked Image]](http://www.florida3s.com/forum/images/smilies/emot-ninjafury.gif)
<--another form to post images.