APM login page, header and front image size

Hi. Does anyone know the size of the "header" and "front image" for the login page. I'm new to the APM and have no experience here. I'd like to stick to basic customization, and want to provide out agencies with the size of these areas, so they can provide those images, and we don't have to play around with resizing. Trying to establish a standard essentially, for an enterprise environment...

Also, is there a way to insert a link on the left side of the login page, under the username and password. Something like a "Registration account and management, click here" Thank you,