IntroductionThe realm of visually encoded knowledge has been a beneficiary of those developments in information and communication technologies which have brought the digital scanner, the optical disc, and the broad-band channel to the commercial marketplace. A number of recent conferences and reviews attest to the mounting enthusiasm with which the heritage management community and other organisations have greeted the resulting opportunities to add value to their holdings of still and moving images (Commission of the European Com-). The exploitation of these opportunities demands more than high-performance storage and transmission facilities, however, and there is a growing perception of the need to address the difficult system design issues involved in visual information retrieval.In Europe the European Commission (through the medium of DG XIII, the Directorate General for Telecommunications, Information Market and Exploitation of Research) and the British Library (via their Research and Development Department) have played a key role in initiating and sustaining significant research programs in the area of image retrieval. Both institutions commissioned reports (Commission of the European Communities, 1988; Petrie, 198X), the publication of which described the technological underpinnings of electronic image banks, identified state-of-the-art applications and future trends, and provided the funding bodies with an informed view of the potential customer base for the fruits of such research. Both bodies subsequently pro-