I have to set up a system for an online-pass generator using barcodes.
The module i developed lets the admins set which codes are available, and when a user requests a pass, the php script generates a jpeg of the pass with a small barcode print at the bottom.
The barcode is generated using: http://www.dafont.com/3of9-barcode.font
Q: Are those barcodes universal? I need to know if the barcode scanner will work on those printed passes.
There are actually quite a few different sets of barcode characters out there. You need to find out which standard the scanners that will be reading the codes will use and find a font or generator that supports that standard.
See http://en.wikipedia.org/wiki/Barcode#Symbologies for a list of them.
mikeschuld has provided good information about barcode printing and scanning. My experience has been that Code 39 is one of the most pervasive barcode formats and every scanner that I have run into has been configured to read Code 39 barcodes by default.