If you allow users to login to your site via both
http://www.yoursite.com and just yoursite.com., then you MUST have your cookie domain (AdminCP > Settings > Options > Cookies and HTTP Header Options > Cookie Domain) set to ".yoursite.com" (no quotes, but note the period at the beginning) or your users will have problems. That should fix the www and non-www issue on your online page.
As for adding an image, add it to the phrase perhaps? Try doing a Search in Phrases, find that phrase and add an image using proper html.