First thing's first, you might want to downsize the image a bit. The maximum allowed size for a signature picture here is 600x150 pixels.

I suggest choosing a high-quality picture of a forest or whatever picture you like, and put it as the background. Then mess around with the layers (window>layers), setting the one with the panda on it to "screen" or something else that looks good. It can produce some really cool effects. If you want to blend two different background pictures together, paste in another picture and use the eraser tool (blurry brush) to fade it out.

What version of photoshop are you using?