The iframe below gets the unique file name from this page, it comes from hidden input ctlSignature_file
The file will get saved on server (under signs folder, which should be 777) with same name as given from this page, hence the submit script submit-form.php will also get same name to show the image.
Name of person signing : and then hit Submit!
You can also click the "Show Me" button to see the generated image below, but make sure you hit "Save signature" first!