core-bundle/src/Resources/contao/forms/FormSubmit.php
public function parse($arrAttributes=null)
	{
		if ($this->imageSubmit && $this->singleSRC != '')
		{
			$objModel = FilesModel::findByUuid($this->singleSRC);

			if ($objModel !== null && is_file(System::getContainer()->getParameter('kernel.project_dir') . '/' . $objModel->path))
			{
				$this->src = $objModel->path;
			}
		}

		return parent::parse($arrAttributes);
	}
public function parse($arrAttributes=null)
	{
		if ($this->imageSubmit && $this->singleSRC != '')
		{
			$objModel = FilesModel::findByUuid($this->singleSRC);

			if ($objModel !== null && is_file(System::getContainer()->getParameter('kernel.project_dir') . '/' . $objModel->path))
			{
				$this->src = $objModel->path;
			}
		}

		return parent::parse($arrAttributes);
	}
Parse the template file and return it as string

@param array $arrAttributes An optional attributes array

@return string The template markup