The Lucerna database uses subject ‘tags’ (keywords) to index the visual content of slides and other images. These can be combined to allow complex searches for images with specific content.
So far only a small minority of the images have been fully tagged, though about half have at least one tag and more are being added all the time.
The search options here find individual tags and/or the categories in which they are arranged, with links to images marked with that tag. For more complex image searching use the search for a slide page.