How to add a full page image or a background image for the home page


I am newbie to elgg and would like to know how I will be able to add a background image for the home page of my website. 

Currently when someone enters the url, they'll be able to see only the login form. I would like to retain the login form but want to add a backgroud image for the full page. This background image should be only for the home page.

Also, could some one please let me know how I can change the text "Welcome to XXXXXX" as shown in the attachment.


Thanking you for your kind help

With regards,