How can i fetch an image url by class name from Webview with Dart

How can i fetch an image src by class name from a WebView in flutter?

 child: WebView(
           initialUrl: shop.link,
             javascriptMode: JavascriptMode.unrestricted,
             gestureRecognizers: gestureRecognizers,
               onWebViewCreated: (WebViewController webViewController) {
                 _controller.complete(webViewController);
        }
        ),