That all depends on the theme and how it is setup to display search results. Some themes will allow for the featured image to be listed in the search results. If that is the case then you only need to set a featured image for each product.
Where this “lives” on the admin UI may move. Make sure that you have all of the option boxes turned on so you can see all the UI options, then search for “featured image”.
If your theme does NOT support featured images in search results this will not work. You may also want to use a WooCommerce specific theme from WooThemes though not all of those will show featured images in search results either.