I am starting to rotate user submitted photos that will fit into our header.
I'd like to encourage you to submit photos that will work without a lot of manipulation. These are very long and narrow photos with some open space to the left for the logo to sit. We usually are able to make photos work by cropping them down to highlight the specific subject we think fits.
I have photos you are free to use, they are optimized .jpg's and scaled to your banner size... with a little extra top and bottom. These belong to me so no issues with copyrights. There are plenty more if you like.