I have locked the other thread an link here to this because the same topic is treated here and needed informations already exists.
The thumbnail of the userpic will displayd with www.deine_domain.de/profilepic.php?u=user_id and the full picture will displayd with www.deine_domain.de/profilepic.php?u=user_id&full.
An examination whether the picture existed, takes place automatic.