删除图片代码

项目中删除图片的代码，希望各位大大能给些安全性的建议。

if(isset($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest'){
			$url = $_GET['json'];
			$url = $_SERVER['DOCUMENT_ROOT'].urldecode($url['picurl']);
			$pictype = array("gif","jpg","jpeg","png","bmp");
			if(file_exists($url)){
				$infos = pathinfo($url);
				if(in_array($infos['extension'],$pictype) && strpos($url,"uploadfile")){
					if(unlink($url)){
						echo json_encode(array("status"=>"1","info"=>L('删除成功!')));
					}else{
						echo json_encode(array("status"=>"2","info"=>L("删除失败，请检查权限!")));
					}
				}else{
					echo json_encode(array("status"=>"2","info"=>L("删除失败，请检查权限!")));
				}
				
			}else{
				echo json_encode(array("status"=>"0","info"=>L("文件不存在或已删除")));
			}
		}