Brian Teeman wrote an article titled "Not All Code is Created Equal" in regards to the licenses for certain code that may be used in extensions that you are using.
A GPL licenses extensions means that you can use it any way you want, (please check the GPL license websites for further clarification, a single sentences doesn't cover the license usage) giving you the freedom to use, study, distribute and redistribute the code how ever you may want.
But how on earth do you check for this?
A developer may be able to work their way through the code and work out what is being used within the extension but a novice may very well not be able to. A person that gets scared of looking or thinking about code will definitely not be able to. The method of checking isn't very hard but sometimes takes a little bit of investigation to work out.
Our very own interns and developers as me this very question when they are installing extensions or developing their own extensions. How do we know and how can we find out?
Ask the Developer
The easiest way is to ask the original developer what libraries and third party code they are using and what is the license for them. A good developer will be able to tell you straight away and these libraries and licenses may also be displayed and listed on their extension website. A person at any skill level can do this and hopefully get the information quickly and easily.
Look For Included Files
Take the example of one of my favourite slideshow components called "Unite Revolution Slider". This slideshow is quick cool in the way it works and the effects that you can get when using it. It makes the home page of your website very impressive.
At first glance you can't really see or tell what libraries that they are using or what the licenses are. This is when you have to dig a little deeper.
If we look deeper into one of these files:
We can see in the top of the file is the license and credits to the original developer of the library.
Now that we have a little more information about the library that is being used we can work out a few things from this.
- Additional documentation about the library
- The license for the library
We can see that the developer has given the github repository of the file, http://eightmedia.github.com/hammer.js as well as mentioning the license and copyright information. In this case the library is licensed under the MIT license.
We now know by looking at this information that this library in particular adds touch gestures to the slideshow and that the MIT license allows us to do as we wish with the library.
Of course this is just one license to one library that the extension uses and there are a few more that need to be investigated.
In the case where the touch gesture library here by Jorik Tangelder wasn't open sources and there was a commercial fee that was attached to using it, you could turn off and disable this particular feature of the extension meaning that it won't be used on the site at all. Since you have disabled and are not using it, you won't need to worry about the license attached to it.
Make Sure You Check
What every the method you use to try and determine the license of a particular piece of code or library, it is important to make sure that you check, and thank you Brian for bringing it up and reminding people about them. For all you know, your website could be breaking the law and the poor developers that originally crafted and tested the libraries that you are using literally are staying poor.