Duplicate the layer. Right click on the layer and press duplicate, then ok. Double click on the background layer and press ok. It will be renamed layer 0.
Step 5
With the topmost layer selected go to Edit > Transform > Flip Horizontal and change the top layers blending option to lighten. The blending mode options are located on the top of the layers pallete.
Step 6
Now you can mess around with the image and do what you want with it.
Try coloring each layer different colors and so on.