core-bundle/src/Resources/contao/widgets/FileTree.php
protected function getPreviewImage(File $objFile, $strInfo, $strClass='gimage')
	{
		if (($objFile->isSvgImage || ($objFile->height <= Config::get('gdMaxImgHeight') && $objFile->width <= Config::get('gdMaxImgWidth'))) && $objFile->viewWidth && $objFile->viewHeight)
		{
			// Inline the image if no preview image will be generated (see #636)
			if ($objFile->height !== null && $objFile->height <= 75 && $objFile->width !== null && $objFile->width <= 100)
			{
				$image = $objFile->dataUri;
			}
			else
			{
				$rootDir = System::getContainer()->getParameter('kernel.project_dir');
				$image = System::getContainer()->get('contao.image.image_factory')->create($rootDir . '/' . $objFile->path, array(100, 75, ResizeConfiguration::MODE_BOX))->getUrl($rootDir);
			}
		}
		else
		{
			$image = Image::getPath('placeholder.svg');
		}

		if (strncmp($image, 'data:', 5) === 0)
		{
			return '<img src="' . $objFile->dataUri . '" width="' . $objFile->width . '" height="' . $objFile->height . '" alt="" class="' . $strClass . '" title="' . StringUtil::specialchars($strInfo) . '">';
		}

		return Image::getHtml($image, '', 'class="' . $strClass . '" title="' . StringUtil::specialchars($strInfo) . '"');
	}
protected function getPreviewImage(File $objFile, $strInfo, $strClass='gimage')
	{
		if (($objFile->isSvgImage || ($objFile->height <= Config::get('gdMaxImgHeight') && $objFile->width <= Config::get('gdMaxImgWidth'))) && $objFile->viewWidth && $objFile->viewHeight)
		{
			// Inline the image if no preview image will be generated (see #636)
			if ($objFile->height !== null && $objFile->height <= 75 && $objFile->width !== null && $objFile->width <= 100)
			{
				$image = $objFile->dataUri;
			}
			else
			{
				$rootDir = System::getContainer()->getParameter('kernel.project_dir');
				$image = System::getContainer()->get('contao.image.image_factory')->create($rootDir . '/' . $objFile->path, array(100, 75, ResizeConfiguration::MODE_BOX))->getUrl($rootDir);
			}
		}
		else
		{
			$image = Image::getPath('placeholder.svg');
		}

		if (strncmp($image, 'data:', 5) === 0)
		{
			return '<img src="' . $objFile->dataUri . '" width="' . $objFile->width . '" height="' . $objFile->height . '" alt="" class="' . $strClass . '" title="' . StringUtil::specialchars($strInfo) . '">';
		}

		return Image::getHtml($image, '', 'class="' . $strClass . '" title="' . StringUtil::specialchars($strInfo) . '"');
	}
Return the preview image

@param File   $objFile
@param string $strInfo
@param string $strClass

@return string