Extract graphics from a web page and display it in a web view

I'm trying to extract some graphics from a web page to show them in a webview of my Android application.

I am basing myself on the example of this post How to display a part of the webpage on the webview android but I still do not succeed, any idea what I'm doing wrong or how I could solve it?

This in my app code:

import android.os.AsyncTask;
import android.os.Handler;
import android.support.annotation.RequiresApi;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.webkit.WebResourceRequest;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import java.io.IOException;

public class MainActivity extends AppCompatActivity {

    WebView mWebView;
    Handler uiHandler = new Handler();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mWebView = (WebView)findViewById(R.id.activity_main_webview);
        //Activamos en JavaScript
        WebSettings webSettings = mWebView.getSettings();
        webSettings.setJavaScriptEnabled(true);
        //Activamos el zoom
        webSettings.setBuiltInZoomControls(true);
        mWebView.setWebViewClient(new MyWebViewClient());
        new BackgroundWorker().execute();
    }
    // load links in WebView instead of default browser

    private class MyWebViewClient extends WebViewClient {
        @RequiresApi(21)
        @Override
        public boolean shouldOverrideUrlLoading(WebView view, WebResourceRequest request) {
            view.loadUrl(request.getUrl().toString());
            return false;
        }
    }

    private class BackgroundWorker extends AsyncTask<Void, Void, Void> {
        @Override
        protected Void doInBackground(Void... arg0) {
            getGraphics();
            return null;
        }
        public void getGraphics() {
            try {
                Document htmlDocument = Jsoup.connect("http://amunet.com.mx/wordpress/index.php/graficas-de-3-tomas/").get();
                //Document htmlDocument = Jsoup.connect("http://datos.botonmedico.com/pruebaJSOUP.html").get();
                //Document htmlDocument = Jsoup.connect("http://darebee.com/").get();
                // Element element = htmlDocument.select("div#div1 > h3").first();
                Element element = htmlDocument.select("div#chart8").first();
                //Element element = htmlDocument.select("div#gkHeaderMod > div.darewod").first();
                System.out.println("Elemento: "+element);

                // replace body with selected element
                htmlDocument.body().empty().append(element.toString());
                final String html = htmlDocument.toString();
                uiHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        mWebView.loadData(html, "text/html", "UTF-8");
                    }
                });
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if(event.getAction()== KeyEvent.ACTION_DOWN){
            switch(keyCode){
                case KeyEvent.KEYCODE_BACK:
                    if(mWebView.canGoBack()){
                        mWebView.goBack();
                    }
                    else {
                        finish();
                    }
                    return true;
            }
        }
        return super.onKeyDown(keyCode, event);
    }
}