J.K Rowling signed book Help?

[irock]

I have been clearing out my loft and all my old books have been up there since we moved in because I have no where to put them... Anyway I fancied reading the Harry Potter Series again as I haven't done in some time anyway yes I started and about a week later I was on Prisoner of Azkaban anyway I have a special edition and a normal book I was about to sell the normal edition on Amazon when I saw inside there was a signature... to the life of me I do not remember where i got the book... I think I bought it on Ebay or something years ago! Anyway is it authentic?

http://imgbox.com/abdBoXOI

[Gunners12345678]

Looks like you have a rare autograph there,
I believe it's authentic,
So lucky,
These days it's impossible to get hers.