Bootleg Photography is the term used when taking pictures at concerts without any kind of official permission
or a photo pass
Much like bootleg taping, the photos are most often for personal non-commercial use, but can also be sold latter on to fans of any given band (I perfer the postcard sized snapshot for a buck).
Many bootleg photographers have shifted to digital cameras due to their size. Also popular is the Cannon Elph, an APS camera the size of a pack of cigarettes that is easily conceilable in a bra or down someone's pants. The best location to shoot bootleg photos from is the first 5 rows.