When you see somebody on a pictures only and judge the person attitude/character, though you never met her/him in real life.
Judge people without knowing them with only a picture of them.
Johnny : Hey man, look at this girl. What an ugly cow, geez. I bet she is a real pain in as a gf
Peter : What? That's is Janine, my cousin. She is a nice person. You and your worthless picture impressions!