Here's an interesting discussion.

http://www.leakylounge.com/index.php?showtopic=42425

[Leaky Lounge » Diagon Alley » Flourish and Blotts » Unfogging Deathly Hallows » "Cover Art Predictions, Part 2"]


Also, on the UK children's cover ("click to expand" version)
Look at the wall just outside the castle door.
It looks like a yellow sketch of some kind in the stone.
Hagrid with his umbrella? I have no idea.