the easiest way is to click Additional Options under where you type your post and attach the photo(s). if it says its too large, instead of worrying about resizing it, i would go to
http://photobucket.com and upload the images there you may have to sign up, upload your images, from there you would do
[img]http://www.photobucket.com/images/link/to/file.jpg[/img]
<-- link to your image between the [img] tags.
if that wasnt clear tell me, ill try to make it more clear.
rl.