Does anyone know how to remove crayon or felt tip from the boards of a hardback book?

It's on the front cover and the covers are the fabric-effect kind. I'm not sure if it's crayon or felt tip, I think it's the latter.

It's not too much of a problem, it's a book I plan on keeping, that I picked up for a few pence at the car boot sale, but other than the marks on the cover, it's in very good condition. It's the complete tales of Beatrix Potter.