Does the Premium Plugin offer a WP MultiSite Version?
The free version works across all Multisite sites easily, just Network Activate the plugin, and enjoy the images showing up in all feeds.
For the Premium version/options, it is a per-site license even under a WP Multisite Installation; so to activate it on N sites in a multi-site network, you would need an N-site license (or several licenses).
We offer multi-site licenses in packs of 5 and 20 with deep discounts, pricing varies. You can upgrade your license at any time within the WP dashboard.