Since you now have the classes assigned you need to put the proper CSS in the CSS Inserts section of the theme options. For your Who am I? menu it would be something like the following.
background: url(path to image) no-repeat !important;
Since your classes have upper and lower case letters you need to make sure to have those correct. Also you may need to add !important as I did in the example.
For more info on sizing and positioning background images check out w3schools.com