Dooney & Bourke Handbag

I was given a Dooney & Bourke handbag, but I am not sure if it's real or a knock off. How can I tell if it's genuine DB? Also if this bag is real would it be worth anything in the future or does the value of it decrease? It's in excellent condition, so if there's a chance I can one day sell it I'll stop using it. Here is a link to the picture of the bag: http://www.zappos.com/images/z/1/0/2/1026568-p-MULTIVIEW.jpg