Davis Remmel writes:
Code 39 is easy to recreate because it only uses two types of lines: wide and narrow. Also, each code has a beginning sequence (thin black, wide white, thin black), and an ending sequence (thin black, wide white, thin black, thin white, wide black, thin white, wide black, thin white, thin black.) To start the coping process, you need the following:
* Sheet of graph paper
* Writing utensil (pen is easier to see)
* Bar/ASCII translating tool (look at Wikipedia article for a table, format 2)
To start, look at the barcode you want to decode. On the graph paper, take record of the barcode using whatever means you feel comfortable with. I use binary, as it is very easy to read.
Davis sadly got a detention for using the decoded barcode info from his teacher’s ID to gain access to his attendance records, but I think this kind of ingenuity should be encouraged, not punished – decode code 39 barcodes by hand.
Skeleton barcode card on Hackszine