Within the php page, display the image. Also do a SQL query or insertion into a text file within the page and leave the variable to be defined within the URL as a $_GET
variable. Then once they open the email email@example.com
will sent the information to the database telling you that "$e" email read the messege.
If you use the php mail()
function, then you can easily find out the subject of the mail, the time you sent it, the time they sent it, the IP they read it on, the IP you read it on, the language of computer they use, and time of which your server read it, and more...
It all really depends what you want to use, php has a ton of ways to determine things about the user.
http://ca.php.net/manual/en/language.va ... efined.php
http://ca.php.net/manual/en/reserved.va ... les.server