Pohutukawa has a beautiful big header image feature. The theme comes with 4 header images to choose from (see Appearance / Header). Of course you can also upload your own header images in the size of 1400×440 pixels (jpg, try to keep the file size small). You can choose to rotate different images on page loads or include one image as a single header image. If your image has a dark color you can choose the white header font color on the theme options page.