you can upload it to Forum Images in the size that it is. You will then need to PM a mod to amend the thread (I can't do it I'm afraid). Glsammy is always very helpful and efficient (sorry Graham
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Failing that you could upload an 800 pixel sized image to the moderated bird gallery. Assuming it's accepted (which may take a few hours) you can then PM a mod and ask for that image to be inserted into the thread.
Matt