A Google search for
css ovelay graphics
I Found this posting at stack overflow with a few examples and links to other articles that describe how to accomplish image overlays:
http://stackoverflow.com/questions/403478/how-to-overlay-images
This ink also looks promising:
http://tympanus.net/codrops/2013/11/07/css-overlay-techniques/
as does this one:
http://www.cssportal.com/blog/adding-image-overlay-css/