Ruby: download Seadragon rendered image from web

Question

I wrote a Ruby script to crawl SFMOMA artwork pages and download artwork .jpgs. I've managed to download .jpg thumbnails at the bottom, but I would prefer to download the high-res center image. Unforunately, the HTML source code doesn't show any .jpg file that I can download. I suspect Seadragon is the reason.

The closet .jpg approximation I found is the og:image .jpg, but it is heavily cropped and not usable.

Example: https://www.sfmoma.org/artwork/91.412

<meta property="og:image" content="https://s3-us-west-2.amazonaws.com/sfmomamedia/media/t/collection_images/6OhBqTH57yLc.jpg">

The bulk of the Seadragon rendering seems to occur here. It seems to be creating the image on the fly?

<script type="text/javascript">
    var viewer;
    $(document).ready(function(){
        sfmoma.artwork();

            viewer = OpenSeadragon({
                id: "zoom_image",
                springStiffness: 10.5,
                gestureSettingsMouse:{
                    scrollToZoom: false
                },
                zoomInButton: "zoom-in",
                zoomOutButton: "zoom-out",
                homeButton: "zoom-home",

                prefixUrl: "https://s3-us-west-2.amazonaws.com/sfmomamedia/static/sfmoma/js/openseadragon/built-openseadragon/openseadragon/images/",
                visibilityRatio: 0.95,
                constrainDuringPan: true,
                tileSources: "https://s3-us-west-2.amazonaws.com/sfmomamedia/media/zoom_tiles/72598/image.dzi"
            });

    });
</script>

How should I download the center piece image? Tell the crawler to right click and save as?