To further suggest you held back a better solution because you assumed the PHP developer was too stupid to understand file hashing is both another insult and ba

To further suggest you held back a better solution because you assumed the PHP developer was too stupid to understand file hashing is both another insult and bad practice. It wasn't a better solution. It was one of many alternatives which came to mind; but I offered them the best solution (serve the graphs from a PHP script) and the easiest solution (run a cron job to delete the old graphs).