If you want to implement licensing module in downloadable php application that need:
Anti-copy schemes just don't work. See numerous previous posts on this site & elsewhere.
You cannot stop people from copying your code.
You could, I supose obfuscate it, mkaing it very difficult for them to change. And, maybe buried in there (or as a necessary .exe, without whcih your code won't function0, you could 'phone home and gradually build a database of IP addresses that are using your code - although I am not sure what that would get you.
Give up on the idea, plan to erly on lawyers if necessary, and put your efforts into developing your product.
I have taken advantage of the latest version of PHP 5.6 which has some new features that can be leveraged in to a licensing and distribution trialware. You can now distribute password protected files and demo applications.
Since there are some best practices to doing this correctly. I am distributing a demonstration website application showing how to setup your apps so they can be launched and checked in real-time for licenses codes just like a desktop application. As a matter of fact the protection extends to the desktop. I am selling the initial code to developers via binpress.com at fhqk.binpress.com. The online demo is http://fhqk.com/informationtechnology/ssl (Simple Secure Licensing)