server/lib/private/preview/image.php

<?php
/**
 * Copyright (c) 2013 Frank Karlitschek frank@owncloud.org
 * Copyright (c) 2013 Georg Ehrke georg@ownCloud.com
 * This file is licensed under the Affero General Public License version 3 or
 * later.
 * See the COPYING-README file.
 */
namespace OC\Preview;

class Image extends Provider {
	/**
	 * {@inheritDoc}
	 */
	public function getMimeType() {
		return '/image\/(?!tiff$)(?!svg.*).*/';
	}

	/**
	 * {@inheritDoc}
	 */
	public function getThumbnail($path, $maxX, $maxY, $scalingup, $fileview) {
		//get fileinfo
		$fileInfo = $fileview->getFileInfo($path);
		if(!$fileInfo) {
			return false;
		}

		$maxSizeForImages = \OC::$server->getConfig()->getSystemValue('preview_max_filesize_image', 50);
		$size = $fileInfo->getSize();

		if ($maxSizeForImages !== -1 && $size > ($maxSizeForImages * 1024 * 1024)) {
			return false;
		}

		$image = new \OC_Image();

		if($fileInfo['encrypted'] === true) {
			$fileName = $fileview->toTmpFile($path);
		} else {
			$fileName = $fileview->getLocalFile($path);
		}
		$image->loadFromFile($fileName);
		$image->fixOrientation();

		return $image->valid() ? $image : false;
	}

}