“The photograph, as we all know,” the Colombian artist Oscar Muñoz has said, “becomes memory at the moment when it not only receives the light rays from the exterior, but is also capable of fixing them. That is the moment when a photograph turns into the past.” The nature of an image is a concept that has long fascinated Muñoz, now 70. When he was in his 20s in the late 1970s, he created charcoal drawings based on photographs, works that questioned photography’s relationship with reality. Today, Muñoz pulls photography into other mediums, a convergence that explores the transitory nature of a picture. In the first U.S. retrospective on Muñoz, more than 40 works address the philosophical dimensions of his art. —E.C.