dom-to-imageを試した

        const openSeaDragonViewerElement = document.getElementById("openSeadragon");
        domtoimage.toJpeg(openSeaDragonViewerElement, { quality: 0.95 })
            .then(function (dataUrl) {
                let link = document.createElement('a');
                link.download = 'my-image-name.jpeg';
                link.href = dataUrl;
                link.click();
            });