Customize Cpanel Theme
From Lunarpages Web Hosting Wiki
With the Webmaster Reseller plan you can customize/brand the Cpanel theme to include your company logo.
To edit the theme log into WHM then click on the Cpanel link, then click on Branding.
The Branding Editor allows you to edit the header and footer images in each theme as well as the main page icons for the style. To do so, you should create a new branding style and then edit it to add your custom images. You can also make an archive of all the images you wish to upload.