Depends what you mean by very large. Reflect can store up to about 50MB/room. For a PNG, that's "fairly large" I guess. We plan to increase this limit in the future.

You'd have to split up the image into chunks of about 1KB each, this would be fairly easy to do by pixels. It would be a fun project to try.

See https://hello.reflect.net/rooms#data-model for more information.