Just create a custom layout with ImageView and add it to your custom Toast:
Toast toast = new Toast(getApplicationContext());
toast.setGravity(Gravity.CENTER_VERTICAL, 0, 0);
toast.setDuration(Toast.LENGTH_SHORT);
toast.setView(yourCustomView); // <- you custom View
toast.show();
Look at this: Custom toast in android : a simple example
EDIT:
ok try this (WARNING ugly pseudocode!!):
 public void yourMethod(){
     new Thread(new Runnable(){
         public void run(){
             final Bitmap bmap = getBitmapFromURL("your URL");     
             runOnUiThread(new Runnable() {
                 public void run() {
                     ImageView img = new ImageView();
                     img.setImageBitmap(bmap );
                     Toast toast = new Toast(getApplicationContext());
                     toast.setGravity(Gravity.CENTER_VERTICAL, 0, 0);
                     toast.setDuration(Toast.LENGTH_SHORT);
                     toast.setView(img); // <- you custom View
                     toast.show();
                 }
             });
         }
     }).start();
 }
 public Bitmap getBitmapFromURL(String link) {
    try {
        URL url = new URL(link);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.connect();
        InputStream input = connection.getInputStream();
        Bitmap bmap = BitmapFactory.decodeStream(input);
        return bmap ;
    } catch (IOException e) {
        e.printStackTrace();
        return null;
    }
}