This paper introduces ImageSleuth, a tool for browsing and searching annotated collections of images. It combines the methods of Formal Concept Analysis (FCA) for information retrieval with the graphical information conveyed in thumbnails. In order to use thumbnails of images to represent concept extents, line diagrams can not be efficiently utilised and thus other navigation methods are necessary. In addition to established methods like search and upper/lower neighbours, a query by example function and the possibility to restrict the attribute set are included. Moreover, metrics on conceptual distance and similarity are discussed and applied to automated discovery of relevant concepts. This paper describes the FCA base of ImageSleuth which formed the basis for its design and the implementation which followed.