I am designing a system that collects a customer's signature once a job has been completed by an engineer at the customer's premises.  Everything is working great, it is a PHP and MySQL based system and the signature is entered using a touch screen and the image is converted to JSON and saved in the database as a string.
However, there may be times when the internet connection is lost or unavailable but the signature still needs to be collected and I was wondering if there was a method that anyone knows of that can save a PHP value locally ready to be uploaded once an internet connect is re established? Perhaps using cookies?
 
     
     
     
    