This code will download image from URL and save to persistent data folder/SD card using AsyncTask - downloadImagesToSdCard will download image from a web server - onPostExecute will set Image to ImageView, and set as background image of a LinearLayout

ImageDownloadAndSave.java

private class ImageDownloadAndSave extends AsyncTask<String, Void, Bitmap>
{
  String img_URL = "http://upload.wikimedia.org/wikipedia/commons/thumb/5/51/Google.png/320px-Google.png";
  String sdCardPath;
  private ProgressDialog dialog;
  
  @Override
  protected void onPreExecute() {
    super.onPreExecute();
    dialog = new ProgressDialog(MainActivity.this);
    dialog.setMessage("downloading...");
    dialog.show();
  }
  
  @Override
  protected Bitmap doInBackground(String... arg0)
  {           
    downloadImagesToSdCard("","");
    return null;
  }

  private void downloadImagesToSdCard(String downloadUrl,String imageName)
  {
    try
    {
      URL url = new URL(img_URL); 
                
      /* making a directory in sdcard */
      //sdCardPath=Environment.getExternalStorageDirectory().toString();    
      sdCardPath = "/data/data/" + getPackageName(); //path that stored application's persistent data
                
      File myDir = new File(sdCardPath,"test.jpg");

      /*  if specified not exist create new */
      if(!myDir.exists()){
        myDir.mkdir();
      }     
      
      /* checks the file and if it already exist delete */
      String fname = imageName;
      File file = new File (myDir, fname);
      if (file.exists ()) 
      file.delete (); 

      /* Open a connection */
      URLConnection ucon = url.openConnection();
      InputStream inputStream = null;
      HttpURLConnection httpConn = (HttpURLConnection)ucon;
      httpConn.setRequestMethod("GET");
      httpConn.connect();

      if (httpConn.getResponseCode() == HttpURLConnection.HTTP_OK) 
      {
        inputStream = httpConn.getInputStream();
      }

      FileOutputStream fos = new FileOutputStream(file);  
      int totalSize = httpConn.getContentLength();
      int downloadedSize = 0;   
      byte[] buffer = new byte[1024];
      int bufferLength = 0;
      while ( (bufferLength = inputStream.read(buffer)) >0 ) 
      {                 
        fos.write(buffer, 0, bufferLength);                  
        downloadedSize += bufferLength;                 
      }   

      fos.close();
    }
    catch(IOException io)
    {                  
      io.printStackTrace();
    }
    catch(Exception e)
    {                     
      	e.printStackTrace();
    }
  }
  
  @Override
  protected void onPostExecute(Bitmap result) {
    super.onPostExecute(result);
    if(dialog.isShowing())	dialog.dismiss();
    
    File image = new  File(sdCardPath, "test.jpg"); 
    if(image.exists()){
      Bitmap bitmap = BitmapFactory.decodeFile(image.getAbsolutePath());
      
      //set image
      ImageView imageView= (ImageView) findViewById(R.id.imageView1);
      imageView.setImageBitmap(bitmap);
      
      //set background
      BitmapDrawable bitmapDrawable = new BitmapDrawable(bitmap);
      main_layout.setBackgroundDrawable(bitmapDrawable);
    } else  
    Log.d("hello", "onPostExecute: image doesn't exists.");
  }
}