Within the Project Editor interface, there is a [Cover Page Image] button on the ribbon of the Reports tab that allows you to set an image for the Cover Page and Proposal reports specifically for a Project:
Here you can set an image that is specific to a Project. This image will be stored specifically for use with the Project.
When you click the [Cover Page Image] button, the following interface opens:
Use cover page and proposal image from global report settings
This is the default and this option will use whatever image you have loaded in your Report Settings interface.
Use specific cover page and proposal repots image in this project
This option will allow you to Add an image specifically for the Project.
This image gets stored in the Project folder automatically and will display in the Files tab of the Project Explorer: