There are some works that arrive in our collection by unknown artists, while there are others that may lack a signature, but can be attributed to a known artist after careful research. Certain genres, such as Meiji-period photography and shunga (erotic prints) frequently fall into this second category. It is difficult to identify early photographers because photography studios did not include credits in souvenir albums, many of which featured numerous photographers. In addition, photographers often bought the negatives of others and reproduced them as a part of their own portfolio. When attempting to make attributions, photographs with no credits are compared to the few that have attributions. Turning to shunga, nearly all ukiyo-e artists produced erotic prints, yet these prints are often unsigned to avoid trouble with the law. For these works, attributions are generally made based on stylistic analysis.