You need to use the Image Tags. Basically copy the URL of where the image is uploaded to (it has to be an online source, such as DakkaDakka's own gallery or another one like Photobucket) and enclose it between the "
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" tags. Typing out the name in a Wiki-style link wont work.
EDIT: Ok the Image Tags worked a little *too* well. Basically click the "Image" when you're making your post (doesnt appear on Quick Post, you have to click the actual button), Copy and Paste the URL, then click the Image Button again. Also, there's a "preview" button to let you test it, so you dont need to actually post the thread until it's good and ready.