People with aphantasia can't form mental images. Sydney Dahl was born with the condition, and in this essay, she describes what it's like.
If I was an art student it may be a problem. But I think it still does affect me, I've just adapted to it. For example, I'm also a double major in creative writing, and my aphantasia still affects me because I'm bad at writing descriptions. Half the time it doesn't cross my mind to give descriptions until I've already handed in a piece. Why would it, I've never needed it. It also sometimes makes reading difficult, people claim to see movies when they read, I just see words.