带水印的PHP GD水ech

Question

我想知道是否有人可以向我提供一种制作方法的教程或源代码，以便使人们窃取我的网站图像并将其嵌入其论坛或网站中时会显示水印，但是如果他们在我的网站上查看它他们不会成为水印吗？

Answer 1

Although Piskvor is 100% correct, I would just like to add how to get the referrer in PHP.

Use $_SERVER['HTTP_REFERER'] to get the Referer header sent from the client. If your website is "www.example.com", the referrer should always have "www.example.com" as the domain name.

Now, to validate the domain name, let's use parse_url() to parse the URL into an array, and extract the different parts. It returns an array, let's call this $url , and to get the domain name, use $url['host'] . Now compare this to your own domain name to ensure that it is on your domain.

Full example:

$referrer = $_SERVER['HTTP_REFERER'];
$url = parse_url($referrer);
if($url['host'] == 'www.example.com')
{
  // Is from www.example.com
}else{
  // Is from other website
}

Answer 2

First, a small detour into HTTP

HTTP is, essentially, the core protocol of the Web - used to transfer hypertext (web pages), images and other media. From the beginning, HTTP was designed to be stateless - amongst other things, this means that it's not possible to find if a request for an image "belongs to" a page or another.

There are basically two workarounds for this in HTTP, but neither is 100% reliable: cookies and the Referer header.

With cookies, you could set a cookie when a user accesses your page, and then check that when serving the images. This may run into concurrency problems when entering the page for the first time.

With Referer , the browser sends in he request for the image an URL from which the image is loaded. Unfortunately, the referer can be easily modified or removed by the user or by security software.

What that means for you

I suggest that you use the Referer field - although it's not 100% reliable, most people won't bother messing with it, and those who will bother, well, they would overcome any other protection.

You'll need to serve your images through a script (eg PHP).

http://example.com/img.php?id=12345 - pseudocode for the check, PHP for the watermark itself:

check if the image with given ID exists, else throw a 404 and end
check the referer - if it matches your site, just readfile() the relevant image and exit
if we're here, referer is wrong - you'll need the watermark:
// PHP code from now on
$original = imagecreatefromjpeg($original_image_path);
$watermark =  imagecreatefromjpeg($watermark_image_path);
imagecopymerge ( $original, $watermark, 0,0,0,0, $watermark_width, $watermark_height, $opacity);
header('Content-Type: image/jpeg');
imagejpeg($original);
exit;

Answer 3

For large images Piskvor's answer is too heavy on server resources. There may also be client caching implications increasing latency unnecessarily.

Instead I would implement the referral detection in a .htaccess file so that all request with either your domain name in the referral or empty referral go straight to the image with no PHP processing. Any other case means a hotlink, and therefore would be served the watermark script.