Well, you could put them in your album, and link to the pic in your album.
Wherever you have the pic, open it in Internet Explorer or whatever browser you use, so if you're using an image hosting crowd like imageshack.com or photobucket.com, etc. you'll probably end up with a url ending in <picname>.jpg or .gif depending on what format you use. If you use the album, you'll have an address ending in ?pic_id=X. Test it by opening a new window and going to that address, if you just see the pic you've got it right.
Copy and paste that address into a post, highlight it, and click on the Img button, which will put the tags around it for you. It'll end up looking like (ignore the spaces)
[ img ]http://www.fto-ireland.com/forum/phpBB2/album_pic.php?pic_id=14[ /img ]
Without the spaces you get:
Play around with it, hit the preview button to see what a post will look like, you can always back out without posting if you've got it wrong.