S2OJ/web/app/controllers/image_hosting/get_image.php

<?php
	requirePHPLib('form');

	if (!Auth::check() && UOJConfig::$data['switch']['force-login']) {
		become403Page(UOJLocale::get('need login'));
	}

	$name = $_GET['image_name'];
	if (!validateString($name)) {
		become404Page();
	}

	$file_name = UOJContext::storagePath()."/image_hosting/$name.png";

	$finfo = finfo_open(FILEINFO_MIME);
	$mimetype = finfo_file($finfo, $file_name);
	if ($mimetype === false) {
		become404Page();
	}
	finfo_close($finfo);
	
	header("X-Sendfile: $file_name");
	header("Content-type: $mimetype");
	header("Cache-Control: max-age=604800", true);