You need the ability to post to some web server. If you don't have one, MLS can provide one for $25 a year, which isn't a bad deal for web hosting. You upload your photos, please keep to 640px wide at the most, and the photo gains a "url" like
http://www.outsidetrains.com/trainsmiley.gif
Now, you just post a message containing that url inside img tags like this:
{img}http://www.outsidetrains.com/trainsmiley.gif{/img}
Only you use [ ] instead of {} so you get this:
Some of the free photo posting sites can work this way. I haven't fiddled with them since I've always had web servers at my disposal.