How to limit a subscription to specific image sizes

[NormsIM]

For a media type (e.g. stock photos) I have several file sizes defined along with prices. e.g.

small = $10
medium = $20
large = $30

I have two subscriptions defined; basic and full. For basic subscription they need to have access to only small and medium image sizes, while full subscriptions get access to small, medium, and large image sizes.

How can I limit subscriptions to only specific sizes?

[admin]

It is impossible to limit subscriptions by the photo sizes.