I'm using the sharepoint bar code generation feature and I was wondering if someone knows which field does it uses to generate the bar code pattern/image, or does it generates that "unique string" on execution time? Thanks
Take a look at the BarcodeGenerator Class members. There is a GetBarcodeImage and GetBarcodeValueAndImage. According to the class documentation: "This member is reserved for internal use and is not intended to be used directly from your code." You can call the BarcodeGenerator constructor to create a new instance. Other than that, the majority of the members and properties of the BarcodeGenerator class are reserved for internal use and not for direct use in your code.
There is a ECM starter kit, that has a sample barcode generator. This is MOSS 2007 version. But, it might give you some insight into how the barcode is generated.
This tutorial will help you as well.
The barcode feature has been removed in SP 2013 (beta 2) and most likely in the final release. If you plan to implement this feature in SP 2010, be warned that once you upgrade to SP 2013 your feature using barcode will not work. The reason this feature was dropped in SP 2013 is because of low adoption. For a list of features discontinued in SP 2013, see: this page.