Our Background Image feature allows you to attach a full page background image to the Cover Page (must not exceed file size limit of 4MB). This image will take priority over the Header and Footer Background Images. For optimal image display quality, please ensure the image being uploaded meets our recommended dimensions and aspect ratio for the configured Page Size. Click here to view our Background Images Knowledge Base article for more details. 

When creating or editing your Template, click on the Cover Page tab and scroll down the page to the Background Image section:

Clicking + Attach Background Image will allow you to upload the image file which meets our recommended dimensions and aspect ratio highlighted above:

The full page Cover Page Background Image will be displayed on the Web View or PDF version of the Quote depending on your selected delivery method: