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:
Click anywhere on the header of the page
Click on the Header Type option on the toolbar displayed
Choose cover to add an header that fills the screen, or choose large banner, banner or title only as required
To add an image to the page header:
Click anywhere on the header of the page
Click on the Change Image option on the toolbar displayed
Choose Select Image
Ensure the Gallery option is selected along the top of the screen
Choose a default image, then click on Select
To insert an image from Google Drive:
Click anywhere on the header of the page
Click on the Change Image option on the toolbar displayed
Choose Select Image
Click on My Drive along the top of the dialog box
Locate the image you wish to add
Click on Select
To upload an image from a local or network drive:
Click anywhere on the header of the page
Click on the Change Image option on the toolbar displayed
Choose Upload
Locate the image you wish to add
Click on the Open button
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.