Recently upgraded my NextGen Gallery setup as well as WP to the latest release, seems the Nextgen Custom Fields (via the plugin of the same name) don't display a field for images any more.
The data however is there and active, if you check the pics on this page, (via the lightbox viewer) you'll see the title under the photo, then a "Related Tags" field. That's the Custom Field in action.
Screenshot is here, normally therte would be a "Primary tags" field.
Many thanks for help to fix this! :)