There is growing interest in, and an increasing number of attempts by, traditional information providers to engage social content creation and sharing communities in creating and enhancing the metadata of their photo collections to make the collections more accessible and visible. To enable and guide effective metadata creation, however, it is essential to understand the structure and patterns of the activities of the community around the photographs, resources used, and scale and quality of the socially created metadata relative to the metadata and knowledge already encoded in existing knowledge organization systems. This article presents an analysis of Flickr member discussions around the photographs of the Library of Congress photostream in Flickr. The article also reports on an analysis of the intrinsic and relational quality of the photostream tags relative to two knowledge organization systems: the Thesaurus for Graphic Materials and the Library of Congress Subject Headings. Thi...