html2canvas/src/proxyimagecontainer.js

function ProxyImageContainer(src, proxy) {
    var script = document.createElement("script");
    var link = document.createElement("a");
    link.href = src;
    src = link.href;
    this.src = src;
    this.image = new Image();
    var self = this;
    this.promise = new Promise(function(resolve, reject) {
        self.image.crossOrigin = "Anonymous";
        self.image.onload = resolve;
        self.image.onerror = reject;

        new ProxyURL(src, proxy, document).then(function(url) {
            self.image.src = url;
        })['catch'](reject);
    });
}