Curator Karen E. Haas discusses how Peter J. Cohen has amassed a collection of some 50,000 vernacular photographs. He recently gave more than 1,000 of them to the Museum of Fine Arts. On display are roughly 300 for “Unfinished Stories: Snapshots From the Peter J. Cohen Collection.” The photographs, most of which are in black and white, span the first three-quarters of the last century. The show runs through Feb. 21, 2016.