Yup, me too. And when I haven't seen the movie, or there isn't one, I often imagine a person, someone I know or an actor, who likes like the character as described in the book, or whose name is similar to that of the character in the book.
Another problem I have is with age. I can't imagine a character getting older, and what's more, I'm 13, so most of the people I know are teenagers. This means that if the protagonist of a book I'm reading is an adult they will often nonetheless be pictured circa 13 years old because the only person I know who fits their visual description is around that age; and yet somehow it does not feel very incongruous simply because my understanding of the book is mainly verbal--often, I use the same person to visually represent two different characters and this never creates a problem, as I always know their names are different.
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