The custom field limitation for free listings in version 1.6.5 isn't working for the images. I set the first two photos in a listing to show for free listings (as well as premium), and the remaining three photos to not show for free listings. When I create a new, free listing, I am able add five photos, and all of them display.
3 Social Links and all 5 images are not the part of the options which were disallowed on setting the Custom Fields. You can hide or disable fields given below for free listings. website, Email, contact no, contact name, Address.
Thanks for the clarification, Nitesh. As a suggestion, please consider graying out the check box (make it inactive) for each field under "Enable for Free Listing" that is not available. That way it would be clear to the admin.