French artist JR has a documentary out in French cinemas, and in it, we are invited to witness the hopes and regrets of the inmates of the maximum security prison based in Tehachapi, California. Tehachapi walks us through a series of projects organised by JR, an artist whose work combines photography, collage and video. With its behind-the-scenes approach, the documentary relates how the austere prison courtyard becomes an ephemeral canvas for the inmates. JR’s team collaborated with inmates and guards to use its signature technique of flyposting to create a giant portrait of 40 men. The artis…