There are a lot of ways you could do this, but most all would involve selecting the blue background, probably with the Magic Wand tool or Select > Color Range. You would then need some white, by filling the selection, or masking the image, or masking a Color Fill layer, or . . .
Then use the Polygon Lasso or the Pen tool to ouline the outer white area, and use this to create a mask.
The first options didn't really work, and the pen tool/polygon is unfortunately just too imprecise, so that the mask becomes a mess /:
If you make the image a layer (opposed to Background)...
You could Select the blue with the Magic Wand as Semaphoric says, then fill with white. Then choose Select - Modify Selection - Contract, and mask or delete the remaining pixels. The Contract operation will give you a nice border the size you choose.
For extra credit, you could use Refine Edge to make the selection more accurate.
Click to see the image against a dark background.
When I selected I used the Magic Wand but not the Contiguous setting, and it picked up a little bit in that curl. When I ran Refine Edge and turned up the Smart Radius some it picked that curl out properly.
I suggest this video to really learn how to make Refine Edge sing:
It says Photoshop CS5 but it's equally applicable to Photohsop CS6.
Alright, I'll take your advice. Thanks again!