If there is an available image proxy then the URL of the proxied image will be included in the proxy_url
key. This can be used to generate thumbnail versions of the image. This URL is the base URL for the
proxy image and it’s up to the client to add any parameters for creating a thumbnail version etc.
But it doesn't say (or link to) anything about what those parameters can/should be
http://popit.poplus.org/docs/api/images/ says
But it doesn't say (or link to) anything about what those parameters can/should be