Note that the "not-an-image.jpg" may not be uploaded to the live server because of persistent security warnings (correctly so)!

A PHP file has JPG file extension

The following anchor links to a file that contains PHP code, but it has a .jpg file extension. The .htaccess file includes the necessary directive to process .jpg files for PHP (although this may not be correct for the current live server).

not-an-image.jpg - a PHP file disguised as an image.

This is the same file, but with a .php file extension: not-an-image.php