Uploading a facebook image is necessary in order to display it within the Facebook Application.
After the image has been prepared, navigate to the aforementioned system location and click "Add Facebook Image" at the top of the page to proceed. Alternately, you can replace an existing image by clicking "Edit" in the grid for the associated image entry.
After an image has been uploaded, click "Edit" for the applicable image to view the the image's URL. This URL can then be referenced in Facebook Text. This step is not necessary if the image is being selected as the main "Facebook Image" in the Facebook App Settings page.