Context options allow you to create one header with multiple images, but control which images show on certain pages.
This saves you having to create a new layout for each page or group of pages that might simply have a different header iamge.
Tthe following options will repeat uniquely for each image (excluding Twenty11/10 images). "image name" will show the name of the image.
Show "image-name" on
A list of pages options will pop up allowing you to select one or more. Selecting these will limit the display of the image to just those pages.
You may also select Custom to specify the page IDs
If you want to show the image on a specific page(s), choose in the previous option, and enter the page IDs here as comma separated list. e.g. 4,73,28,19.