Hi guys and girls,

You may have received the Spotify "Your year in music" mailing recently, which have left me dumbfounded. I've dived into their code and noticed that the image is changed based on a parameter in the URL: http://mi.news.spotifymail.com/p/rp/ada6f7ae2d4cf105.png?mi_uniquetracks=1830

Change the last numer in the URL and you get a different image. Now the interwebs isn't really helping my find an answer, so I turn to you, Litmus community. Can you explain how this is done? Is it a PHP-script that generates an image based on the parameter, or is it something else entirely?

I hope you can help me out.

Kind regards,
Kevin