I found a caption of a painting in a book which says:<br/><br/>"The Byzantine emperor Basil II triumphant over the Bulgar tribes, in an image based on an 11-century miniature from St Mark's Basilica in Venice."<br/><br/>Why is there "an image", "an 11-century miniature" in the caption?<br/>Shouldn't be "the" there? We say about an unique thing.