San Francisco (AFP) - Alcatraz is perhaps the world's most famous prison. And Ai Weiwei is arguably China's best known artist. Now they have come together in a viscerally powerful show in the notorious former jail.Visitors to the island prison set in San Francisco Bay can browse seven multi-media pieces, several referencing Tibetan independence campaigners but others including Edward Snowden and Chelsea Manning.The "@Large: Ai Weiwei on Alcatraz" exhibition, which opened at the weekend and runs through next April, "raises questions about freedom of expression and human rights that resonate far beyond this particular place," a spokesman said."Folks come out to the island all the time to Alcatraz and they hear about the gangsters, they hear about the imprisonment.