Here is a navigational trail in the instance you do not know offhand where to find this setting:
Joomla Admin ---> Components ---> K2 ---> Categories
You can navigate there with the dropdown menu within the admin backend.
From here you'll navigate to the category you would like to adjust these rules for.. i.e; 'WebStore'
Within your category you'll notice a navigational pane with these options:
> Category item layout
> Category view options
>... etc etc
Within the Category view options you'll see a setting to Hide images.. I typically hide both the Category and and the Sub-category images as they are generally not needed. Also, it is usually easier to adjust all options within Categories for listings etc from the Category Options screen. You can apply that all your items (menu items as well) use these rule-sets. This keeps you from backtracking to view settings of various listings and items.. especially on larger sites.
Hope this helps.. and I only clarify on this solution as I see the image is still there for your category folders.