The Book of Life

Alright so you're using photoshop, right?

You make a new layer on top of everything and you put a texture on top of it. I like to unsaturate it just to keep from adding a dingy look where I don't want one. If your picture wasn't so busy I'd recommend *Inthename-Stock but that might make it too busy, so instead I'd go for a relatively flat texture like stone or stucco. You can find a whole mess of textures on deviantart by going:

browse - catagory - resources - textures - all textures

Set the texture layer on multiply and lower the transparency to about 10% or less so that it's almost not there, but present enough to add a sense of unity. Duplicate the later. You then can use the lasso tool to highlight the center area in a rough oval, feather the selected area (under "select" on the tool bar), and delete. This will create a graduation from higher transparency towards the edges to very faint transparency in the middle, provided both layers are on multiply. It might give a papery look to your picture, depending on what texture you use, but it should also make it all look like a whole.