Intentionally posing in other people's photos, for a later surprise.
Usually people making funny faces in the background, without the knowledge of the main subjects of the photo.
Photophobia is a fear of, or adverse physical or psychological reaction to light. Whether from rapid change of light intensity, or sudden burst of bright light, as from a camera flash. Not to be confused with heliophobia, which is a fear of the Sun.
When we went to the laser light show, Jon must've got a case of photophobia. He puked and had a seizure.