https://www.prometheus-bildarchiv.de/

Thanks to the number of objects, the variety of its chronological and geographical spectrum, and the ease of use, the Prometheus Bildarchiv is one of the best online image databases for art history, especially superb in respect to sculpture. Access is not free, but an individual license costs only €20 per annum. High-quality images can be easily downloaded and are to be used exclusively for individual research and teaching (publication of the images is strictly prohibited).