Header With position:fixed is not staying in front of images

I am experimenting with customizing a WordPress template and I have things close to the way I want them. One of the last issues is that I have a header that has position:fixed so it floats at the top the whole time. It works but when it floats past an image, it goes behind the image. How do I get it to stay in the foreground the whole time while scrolling? Here’s a link:

http://miller-media.com/glossandglamblog/

Thanks!