artnightstyle Hi
-You may enter page class suffix assuming bg-1 for specific menu item taking reference from here and here
-Thereon, add this to custom.css file and change background image path accordingly:
html.bg-1 body{background:url(/joomlart/ja-space/images/joomlart/others/our-team.png) no-repeat;}
Note - Do ensure to add space infront of page class suffix being entered
In similar fashion using the page class suffix method, You can have the same replicated for other menu items using different class suffix
If still unable to get the desired result, Can you add your admin details in edit fields in order for us to take closer look.
For reference, You can follow thread post (5 point) procedure.