to this layer, use the liquify tool and expand the back of the sneaker to the borders of the layer. then add a mask, but to this mask, give image-adjust-invert. when you invert the mask, everithing you liquified disapear. now take again the free splash brushes, but use the white color, and start making your art. in a different layer make the shadow of the sneaker with a opacitly of 75%. create the backrground level and give it the color you like. and thats it.