know somebody by sight

know (someone or something) by sight

To recognize someone or something based solely on appearance (without knowing any other information, such as a name, etc.). Even after working there for a year, there were still some co-workers I only knew by sight. I'd know the place by sight, but I don't think I could tell you how to get there.
See also: by, know, sight

know somebody by ˈsight

recognize somebody and know who they are, without having spoken to them: I haven’t actually met Dr. Galston, but I know him by sight of course.
See also: by, know, sight, somebody