core-bundle/src/Resources/contao/elements/ContentImage.php
public function generate()
	{
		if ($this->singleSRC == '')
		{
			return '';
		}

		$objFile = FilesModel::findByUuid($this->singleSRC);

		if ($objFile === null || !is_file(System::getContainer()->getParameter('kernel.project_dir') . '/' . $objFile->path))
		{
			return '';
		}

		$this->singleSRC = $objFile->path;
		$this->objFilesModel = $objFile;

		return parent::generate();
	}
public function generate()
	{
		if ($this->singleSRC == '')
		{
			return '';
		}

		$objFile = FilesModel::findByUuid($this->singleSRC);

		if ($objFile === null || !is_file(System::getContainer()->getParameter('kernel.project_dir') . '/' . $objFile->path))
		{
			return '';
		}

		$this->singleSRC = $objFile->path;
		$this->objFilesModel = $objFile;

		return parent::generate();
	}
Return if the image does not exist

@return string