"fun fact: Vampires actually WOULD show up in modern day photos and mirrors!"

R/ST:

back in ye olde times, mirrors were made with silver. And silver, being a "holy" or "pure" metal would not reflect the unholy image of an undead creature. Thus, no reflection in mirrors. As for photos, olde timey cameras used all manner of chemicals to create the image, and those chemicals would often include some amount of silver.

Modern day mirrors are made with aluminum behind the glass, not silver, so a vampire's reflection would show up no problem. And since modern cameras are all digital, they would show up in photos and videos too!