yeah, the forum sort of bastardizes images because of the way the preview database works.
you can...
attach the pic to your post... submit the post.
then view your post and click to load the pic. you can then right click the actual picture (you will get the direct .jpg link instead of the database referral)
then edit your post and paste it in your img brackets
alternatively (and what I do now) is post the picture to imgur. Imgur then has a SMF BBcode forum direct link already formated with img brackets already attached to it you can paste into your post.