Piano Black: add image div inside of header

hello, I would like to add another image in to the header of the Piano Black theme. As it sits now I have a image, with the header’s black background saved to one png file. What I would like to do is save the background as just one layer of black with the round corners at the top as a png. Then add the image of the four guys as a div on top of the background saved as a jpg. This would give me faster load times for the header. You can see the site here.

How would I go about adding an additional div for just the image?

Thank you.