code: public function addPreviewImage($row, $label)
  	{
  		if ($row['screenshot'] != '')
  		{
  			$objFile = Contao\FilesModel::findByUuid($row['screenshot']);
  
  			if ($objFile !== null)
  			{
  				$rootDir = Contao\System::getContainer()->getParameter('kernel.project_dir');
  				$label = Contao\Image::getHtml(Contao\System::getContainer()->get('contao.image.image_factory')->create($rootDir . '/' . $objFile->path, array(75, 50, 'center_top'))->getUrl($rootDir), '', 'class="theme_preview"') . ' ' . $label;
  			}
  		}
  
  		return $label;
  	}
docs: Add an image to each record
  
  @param array  $row
  @param string $label
  
  @return string