So this is a thin client that interfaces with processes that run on the server? meaning the state of the image and what has been done with it has to be kept in

So this is a thin client that interfaces with processes that run on the server? meaning the state of the image and what has been done with it has to be kept in sync between the client and the server - this isn't pure client 'html5' using canvas et al What language/env is the server-side portion of this?