Wikipedia explains: Those who photograph cosplayers are called cameko, short for *Camera Kozo* or *Camera Boy*. The cameko give prints of their photos to the cosplayers as gifts. In this case, since we're in the XXI century, we no longer give "prints" but share them online for everyone to see.
Check the galleries! I have +14,000 cosplay-related photos. See the list for past events dates, and follow the links to see the pictures.