自动获取显示我的图片的网站的网址？

Question

I've been trying to get the URL (including GET parameters) of a site that is displaying my image. This is because I want to extract one parameter of the URL.

A friend told me that she knew someone that could achieve this, but I don't know if he was doing it with an image. Also I don't think I can do it with a link because when going to external sites it will appear a warning page saying that you're being redirected outside, so if I put a link to my page and someone clicks, I will get the referrer URL of redirection warning page. I can't assure if my friend was telling the truth about this, but it's very likely that it was true.

All I could get with the image was the IP and other things of the HTTP header, but the referrer part is empty and I thought that the referrer contained the full URL I'm talking about.

This is what I have tried. First the img tag in the other site in BBCode:

[img]http://______.com/get_image.php?i=myimage[/img]

And in my site this script in PHP, although any language that does the work would be good for me:

<?php
// Get name of image to be displayed (non-sanitized here for simplicity)
$filename = $_GET["i"];

// Here I want to get the site where image is being viewed
if (!empty($_SERVER['HTTP_REFERER'])) {
        $visitor_url = $_SERVER['HTTP_REFERER'];
} else {
        $visitor_url = "none";
}

// And write the referrer to a file just to test if it works
$fp = fopen('referer.txt', 'w');
fwrite($fp, $visitor_url);
fclose($fp);

// Eventually display the image
header('Content-Type: image/png');
readfile($filename . '.png');
?>

So my questions are:

1. Is it possible to get full URL of a site that is displaying my image?
2. If not, is there any other method to get the full URL?

Thank you in advance.

Note: I don't have any permision in the other site where I'm posting the image, I'm just an user there. Please tell me if I'm missing something or I have to ask this in another way, I'm new to StackOverflow.

Answer 1

I fixed this problem by switching my site (where image is hosted) to HTTPS. The code in my question was doing its job correctly.

It looks that HTTP_REFERER was blank because of it coming from an HTTPS site and my site being HTTP it would always send it blank. I was aware that it could be a problem, but didn't make much sense for me because HTTP_REFERER was also blank when coming from another HTTP site (which I think it's not normal) so I thought the error was in another place.

Usually HTTP_REFERER is sent when it comes from and goes to:

1. from HTTP to HTTP
2. from HTTPS to HTTPS
3. from HTTP to HTTPS

But it's not sent when it comes from and goes to:

1. from HTTPS to HTTP

And in my case, I don't know why, it wasn't being sent from HTTP to HTTP which was confusing me.