Bit Of Help Needed

Just had a thought for tracking copies of my php game engine online ina hidden way. Basically I've already had people taking PGE and intending to convert the source code in to a premium game instead which requires a license to do. I need a way to track all copies of my engine online. I don't really want to have some form of online database used to operate the engine because that would cost me a lot in bandwidth. My thoughts were to conceal certain data in the page headers and source code then use a search engine to search through source code instead of browser output but it keeps bringing me round to code search instead which isn't what i'm after. Anyone got any thoughts on how to do this? Obviously it can't be too obvious otherwise people could null it out, but i've got ideas and methods to disable a script after i've found one running premium without a license.

Should be easy in C, but you could try my trick with php too.If it's an online game, people need to connect to your server.I would say that a character has to log in a file that he is present and his IP recorded.Your program reads from your server the value of a pointer, and branches to this pointer at a crucial moment of the game.A premium game will not connect to your server, so the pointer will have another value and at the crucial moment the game will go to a stupid demo instead of branching to the interesting part of the game.Cannot be found easily because this is not a bug, the game will be functional, simply your free users will have a nice game and the persons who bought the stolen premium code will have a useless long-lasting demo.Of course, in order the trick to be not so obvious, the pointer should be initialized with a read value, for instance "time of the day", and your moving algorithm on your server should take this into account.What do you think about that? If it works you should invite me for a cup of coffee.

I've actually come up with several working methods hidden deep inside the code which enables me to track copies of PGE without transmitting personal data across the web or using my own site to complete the source.

Obviously though it would be kinda counter-productive if I listed all the methods on here because anyone who came across this post would know exactly how to nullify my scripts. Instead I'll list a few different methods you can use to protect your own scripts from piracy should you need it. So including yordans method above here are some variations and alternatives.

CodeLock - http://forums.xisto.com/no_longer_exists/
This natty piece of software design is used to both encrypt your php source code and track the use of your source code online. The php files are decrypted off a file on your own server to prevent people just decrypting them off their own server and nullifying the script.

Image Calling
This method is where you place an image (or several) in a script then when setting the src="" part of the image you set it to a php file on your own web server eg. src="http://forums.xisto.com/no_longer_exists/=;. The file checksite.php then retrieves the contents of the $_GET variable 'site' and writes it to your database for you to investigate later on.

Source Guardian - http://www.sourceguardian.com/
A little pricey but this is an application similar to CodeLock however it boasts a few more features such as setting the decryption key to use the current domain and so on as well as other parts of they key. This is useful if you are looking to lock your code to a particular domain name.

ionCube PHP Encoder - http://www.ioncube.com/
Yet another method for encrypting your source code. I haven't had any experience with the demo on this one so I can't give you an honest opinion.

POBS - http://pobs.mywalhalla.net/
Another encryption package however this one is open-source and free.

If you want me to go in to any kind of detail on the above methods and software then just let me know.