Good
As a cover this picture works really well. I like the action we can see on this picture, even though it's (obviously) just a still frame.
But the colours would work on a cover as well. Ok, maybe it would be a tad bit TOO dark on a book cover, but I like book covers that aren't overloaded with various characters or huge letters best.
The character design is good, too. The propotions are realistic and the clothing fits quite well.
Only thing I would change is the ear. Like Coop already suggested, I would hide it (at least partially) behind the hair.
{ Review Request Club }