This week a revised Facebook ad policy went into affect. This change limits the text overlays on timeline cover images and newsfeed ads to no more than 20% text.
They will only approve ads that are at least 80% image. (This even includes text within your logo). You can still post images on your business page that have more than 20% text, however, you will not be approved to promote those posts in newsfeed ads (i.e. promoted posts).

This image from ShortStack demonstrates exactly what 20% of an image means.

Other restrictions on cover photos include:
• URLs
• Calls to action
• Contact information
• References to Like or Share your Page
• Price or purchase information
Facebook is already enforcing these new rules. They have even developed a tool that will review images to make sure they are compliant with all regulations.