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Are you trying to put a picture in your post or are you trying to add an avatar? Gary's comment is relevant for the latter. For the former, you can use the "Save for web" option, and then use the sliders to make it sufficiently small. :)

Better yet, though, host it at photobucket.com or flickr.com or the like and then inline it with tags like [ img ] your url here [ / img ] (delete the spaces).

:)
 
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