Way to complex and in-effective
A WCF cronjob is called every X minutes, gathering all neccessary data and re-creating the image. Since the image will have a static name, the link will not become invalid. Thus if the cronjob is called every 5 minutes, the script will re-create the image maximal 288 times per day. Imho is it enough to call it every 15 minutes, reducing total calls below 100 times per day. In reality the board is not visited all the time, so the total amount of cronjob calls is reduced again which does not affect the stats: no user online, no possible change.
This way only the image itself without any additional script is called all the time, saving an enormous amount of performance.