the linkto setting determines what happens when you click on a link. By default, the link will open the related post. We have a free addon for colorbox that is specifically for images in the media library and open up the full sized images in a lightbox slideshow. When using colorbox, the target and openwindow settings will be ignored since clicking on the grid opens the light box instead.
(default) open the page for the relevant item (do not confuse this with the post type)
– open the images in lightbox (requires the colorbox plugin)
Colorbox theme. There are 5 themes. Colorbox defaults to cb_theme=3. Do not load more than one theme on the same page as these are style sheets and only the last loaded stylesheet will be applied to the colorbox.
[featured_image_pro post_type='attachment' linkto='colorbox' cb_theme=2]