Hi samnasr,
The skin you are editing was optimized for one-click color changes in the footer.
If you would like to have the ability to change the footer background to a custom image, open your skin in "Advanced" mode and find the lines that look like this:
/*:Footer ~*~*/
#footer{/*:Footer Font */
color:#ccc;font-size:12px;font-weight:normal;font-style:normal;font-family:inherit;}
#footer .widgettitle{/*:Footer Titles Font */
color:#eee;font-size:22px;font-weight:normal;font-style:normal;font-family:colaboratelight;}
#footer a{/*:Footer Links */
color:#ddd;text-decoration:none;}
#footer a:hover{/*:Footer Link Hover */
color:#fff;text-decoration:none;}
#footer{position:relative;background-image:url(../images/black53.png);background-repeat:repeat;background-position:0 0;}
#footer>.multibg>.multibg{position:absolute;height:339px;width:100%;background-image:url(../images/footer.png);background-repeat:repeat-x;background-position:center top;}
#footer,#footer>.multibg>.multibg{/*:Footer Background Color */
background-color:#ab1111;}
#footer .widgettitle,#footer .widget li,#footer .widget a{/*:Widgets Border Color */
/*border-color:inherit@;*/}
/*:Footer End ~*~*/
Change them to the following and then save changes:
/*:Footer ~*~*/
#footer{/*:Footer Font */
color:#ccc;font-size:12px;font-weight:normal;font-style:normal;font-family:inherit;}
#footer .widgettitle{/*:Footer Titles Font */
color:#eee;font-size:22px;font-weight:normal;font-style:normal;font-family:colaboratelight;}
#footer a{/*:Footer Links */
color:#ddd;text-decoration:none;}
#footer a:hover{/*:Footer Link Hover */
color:#fff;text-decoration:none;}
#footer{/*:Footer Background */
background-image:url(http://amjcm.com/wp-content/uploads/2012/01/RED-BACKGROUND-GRADIENT-4.png);/*background-color:inherit@;*/background-repeat:repeat;background-attachment:scroll;background-position:center center;}
#footer .widgettitle,#footer .widget li,#footer .widget a{/*:Widgets Border Color */
/*border-color:inherit@;*/}
/*:Footer End ~*~*/
Now when you open your skin in the normal edit mode you should have the option to easily upload any image you like for the footer.