There are many more photos and examples in these books:

Gangs and Their Tattoos : Identifying Gangbangers on the Street and in Prison.

Bad Boys and Tough Tattoos: A Social History of the Tattoo With Gangs, Sailors and Street-Corner Punks, 1950-1965.

Prison Tattoos.

Angeleno David Cavado, 19
From Houston Chronicle/Dave Einsel

18th Street Gang tattoo
From Washington County Sheriff's Office

Aryan Brotherhood Tattoo
From Security Threat Group

Mexican Mafia Tattoo
From Security Threat Group

Crip Tattoo
From Florida Department of Corrections

Red Blood Dragon Tattoo (Bloods)
From Pointman/gangtattoos.com

Check out these books on tattoos.