use the “featured image” for a menu item
if you do not have this options it’s either hidden (go to “screen options” at the top of the page to enable/show it) or your theme does not have thumbnails enabled (tell the author about it. not my fault) if the auther doesnt want to or cannot do anything about it, you can also try just to put the following code at the bottom of your themes function file (before the closing ?> if any )

add_theme_support('post-thumbnails');