Each page in your site has a page header that can be formatted to match the overall style of the site, or by adding an individual background image to the header. Various header styles can be used to ensure your pages look as you want them to.

To set the header type:

To add an image to the page header:

To insert an image from Google Drive:

To upload an image from a local or network drive:

To remove an image from the page header, click anywhere on the header, then on the Reset button on the toolbar displayed. 

By default, Google Sites will change the colour of your image to optimise it to display text clearly over the image.

If you do not wish to optimise the image, click on the icon to Remove readability adjustment.