image - img tag html run php function automatically without trigger it

I created a tracking function which is used to track if user open email that i sent by using img tag.

The code is like below:

<img src="' . $domain . "/a/Specialopenemail.php?&p=" .$message_id . "&m=" . $memberid .'" width="1" height="1" />

It works fine for the first time, but after several times sending emails, the img triggered automatically and assumed all the users already open the email eventhough they not opened it.

I try using clear cache and sleep function but it doesn't seem to work. I searched over the internet but till now the method of track email is still the same.

Solution:

If the image is caching, and therefore loading in the email but not making a call to the server, add a timestamp to the URL to make every email image unique:

<?php

$img_tag = '<img src="' . $domain . '/a/Specialopenemail.php'
  . '?p=' . $message_id . '&m=' . $memberid 
  . '&ts=' . time() . '" width="1" height="1" />';

?>

$img_tag looks something like:

<img src="http://example.com/a/Specialopenemail.php?p=324&m=27&ts=1667494626" width="1" height="1" />

1667494626 is an example what is returned by . time() returns: