Shortcode: 3 pictures of gallery 1 in random order

I try to add a shortcode to display 3 random pictures of a specific gallery.
The following did not work, but displays the full gallery:

[ngg_images gallery_ids="1" order_by="rand()" images_per_page="3" disable_pagination="yes" display_type="photocrati-nextgen_pro_mosaic"]

Is this not possible with the mosaic template?