You can't delete them once they have been posted unless you are a moderator and remove the post; or get one of the moderators of the board to remove the post in question.
If you are talking about an image in iHub image file, there is a little blue "Hide" in the upper right by each photo that will delete it from your Image List. However, if the photo is in a post, it will remain in the post and once again, you need to have the post removed.
Sometime if you ask nicely, admin will remove a post. However, it usually has to be something worthy of being removed.
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