From a reader (more on vampires):
Let me add a bit of tradition, if I can, to the whole vampire/photographs/mirrors issue in hope of clarifying things.
The traditional folklore reason why vampires can’t be seen in mirrors or photographed comes down to the same rational: their image cannot be held in silver. Why this is so (again, speaking of folklore) is that, in recompense for the injury to silver’s reputation due to the 30 pieces of silver paid to Judas to betray Jesus, God gave the metal power against evil and all manner of unnatural creatures. Hence the power against vampires, hence the mirror/photograph thing.
Wacky? Sure. But so is a lot of folklore.
Along those lines, it is therefore entirely logical that they show up on digital media, where no silver is involved.