The current novel I am reading is about a vampiric private investigator. True to common lore, she does not show up in mirrors. And she does not show up in photos, either, but that may or may not be part of lore. Let me explain.
Vampire mythology appears to have been popularized after the introduction of mirrors, but long before the introduction of photography. Earlier cameras took images by using a series of mirrors to focus light. Digital cameras, however, don’t rely on mirrors (as far as I can tell), so the idea of a vampire not appearing in modern photos no longer makes sense. Perhaps without realizing this, Charles Stross addresses the camera-ready vampire in his Laundry Files series by allowing his vampiric characters to dress and primp using laptop cameras even though they do not appear in mirrors. I honestly don’t remember if he ever went into this apparent mystery in his books, but it really does make sense, once you remove mirrors from cameras.
As authors, we strive to keep our characters in tune with their times and/or the rules we established for their worlds. For fantastical fiction, the writer either follows the rules of similar worlds or creates a new set of rules governing the environment–natural laws, if you will, that govern that world. As readers, we can suspend belief in the natural laws of our own world and place ourselves in the environment of the author’s world as long as the rules are consistently followed within that world.
In terms of lore within our own world, certain characteristics or law-breaking mechanisms are acceptable if the lore itself is accepted. So, with vampires, we accept that their images cannot be captured by mirrors; although photographs using mirrored cameras would result in no image of the vampire, digital cameras (which use no mirrors) should now allow the image of the vampire to be captured.
This was just a passing thought…