You, my brown-eyed Frodo

[Eönwë]

Originally Posted by Galadriel

No, that's quite common. Many people have a hard time conjuring up a face.

I remember I heard somewhere that all the faces you dream of or can imagine are made up of real faces you've actually seen in real life, even if subconsciously. Maybe this would explain it? (I also find it hard to do)