The forum code does absolutely nothing with [IMG] tags, so if you leave them in they'll display, which looks a bit ugly. If the image shows anyways, it's because it's reading the URL between the tags, and as far I've seen that shouldn't be any different than the so-called "direct" link - which should be what you want.

If you come across images that don't work based on the URL, then what you want is the proper HTML code, which will look like

you actually dont have to remove the brackets! just copy and paste as is.

You can do it the way Mike said too but ive found sometimes it doesnt work so best to just copy and past the "IMG" code like i circled in my post.