title: Most efficient barcode to store a GUID
body: <p>I have a system that I'm working on at the moment that requires users to log into the system, and the client wants to use a barcode scanner and cards to keep prices down. (Yes username and password cheaper, but she wants a card type solution so she gets one.)</p>
  
  <p>All my data uses GUIDs as key fields, so I'd like to store the GUID directly on the card in the barcode.  While its simple enough to code it as 3 of 9 its not going to be the most efficient use of space. </p>
  
  <p>Is there a best practice or most efficient method for storing GUIDs in a barcode? I'd have assumed that since there's a consistent length, and depth to the data there would be a standard, but I can't find it. Would be easy enough to generate my own - control char either end and then binary data between, but would like something that standard readers will know how to interpret.</p>
  
  <p>Any help gratefully received.</p>