So I matched the width of my images to what was in the theme by default (1300px). What resolution are you running? It will be very hard to get the pictures wider than that while without stretching them vertically as well. Any ideas on a good way to do this
My screen is set to 1440 x 900, but if 1300 is the size of the images, and you want that as the largest screen size, go to Atahualpa Theme Options -> Layout -> Layout MAX width and set it to 1300.
Right now as I make the screen wider, the picture expands and the center expands until I hit 1300, then I keep expanding and header image can't get any bigger, but the layout can, so the blog title floats off the picture.
Not sure what browser/os you're using so I'll be generic. Open a browser to the site. Click the box on the browser so it's not full screen but you can resize the window. Now slide the window partway off the screen and then manually make it wider checking out the header.
Once you add the max width, if someone resizes the window greater than the size you name, they will get an expanding margin past that size. If you want to see an example you can look at my site (http://zenofmud.org
). Another way to see the effect is to set the max width on your site to ...say 500 and go look at it.