Miskatonic
Auror
I think visually so I have a very good idea what my MCs look like. Hair colour, build etc...
I will come across an image somewhere,sometime the whole person, more often than not a face, occaisionally just a part of a face. I store those images away [in one big pit of images - that are deliberately not storted] for use later.
When I come to a story I start assembling the characters in my head and usually a memory of a saved image comes to to the front as being exactly what I need.
For one recent MC, the character's image is the eyes of The Stranger [Clint Eastwood] in High Plains Drifter. That's it just those thin half closed sharp eyes taking in everything...
Clint Eastwood during his spaghetti western days is also a big influence on my MC. The man with no name, etc.