From the Facebook Help Centre- Cover images must be 399 pixels wide and may not contain:
- Price or purchase information, such as "40% off" or "Download it at our website".
- Contact information, such as web address, email, mailing address or other information intended for your Page's about section.
- References to user interface elements, such as 'Like' or 'Share', or any other Facebook site features.
- Calls to action, such as "Get it Now" or "Tell your Friends".
Google+ cover photo specs:
Facebook cover photo specs:
- Width: 851 pixels
- Height: 315 pixels
If you want a detailed idea of how the Facebook cover is broken down have a look here:
Despite Facebook's rules you can still be creative with your cover photo. You can create your own mini cover promos without breaking the rules with your work. This is my
current Facebook like page cover:
|© Holly DeWolf- http://www.facebook.com/hollydewolfstudios|
If you need more ideas then start having a look on Google+ and on Facebook to see how many illustrators and other businesses are utilizing this new format on both sites.