1. CDN has direct access to the filesystem

    draws images directly from the filesystem
    or in some other background process
    does not give a chance to our plugin to deliver images in any way

    DOESN'T WORK



2. CDN requests for images over http

    images are requested by the CDN from the WordPress installation in the same way a browser would request them
    in this case what we need to make sure is that the CDN transmits the original requesting browser's device dimensions to the WordPress installation
    this is possible via url parameters which are set on the image source urls in the frontend (either via javascript in the browser, or via HTML regexp img src substitution in the server side)

    WORKS !!!



3. CDN is using a different subdomain for images

    although this could technically fall either under cases 1 (CDN has direct access to the filesystem) or 2 (CDN requests images over http), even if we are under case 2, these kinds of setups usually do not take image url parameters into account, thus totally bypassing the plugin

    DOESN'T WORK