Art historical photo archives (or photoarchives) are collections of reproductions of works of art that document paintings, drawings, prints, sculpture, architecture and sometimes installation photos. They are essential resource tools for the study of art history. Image collections deepen understanding of specific objects of art and the careers of individual artists as they also provide the means for a comparative approach to the study of artists’ works, national schools and period styles. The documentation that accompanies the images can also reveal patterns of art collecting, art market fluctuations and the changeable nature of public opinion. Photo archives build their collections and gather documentation for the works of art they record through purchases, gifts and photography campaigns