i) Open ‘Screen Options’ of your ‘Menus’ page and enable ‘Description’ and ‘Title Attributes’ from there.
ii) Now use the ‘Description’ field of the Drop-down menu to insert your image URL there and also you can use the ‘Title Attributes’ field to get a sub-title for that menu item.
Once done, click on the Save Menu button and you are done.
Click on the image below to enlarge it:
