Multiple ways to do this. I'd use tinypic (tinypic.com is self-explanatory when you go there) when you upload your photo, it will give you multiple links to use. You want the one that says "Forum and Message Boards" (It will have the [IMG] parts.) You could also use the forum version by clicking the plus beneath your post and selecting the file from your computer. Keep in mind about the file limits, your photo won't go through if you exceed them. (It will tell you when this happens)

Hope this helps!