Photography was central to Warhols art and he used it throughout his career, pushing the medium to its limits. His commissioned portraits usually began with a series of Polaroid images, and several collections of his photographs were published in book form. His last exhibition in New York was of photographs sewn into grids of repeated images. Typically, the photographs are used as a material to be manipulated rather than as an end in themselves. Combining needlework with photography, these works blur the boundaries between the hand-made and the machine-made.