The potential for error is larger if you use pure image matching, that's the only thing
If you scan the image with a barcode reading utility it will use the checking algorithm and the last digit (the algorithm varies per barcode standard, but they're all fairly trivial mathematically) to make sure it's read the code correctly, and spit out an error if it hasn't.

Using image matching means you're not using this handy feature of barcodes, hence the increased error potential. You definitely want to be summing the check digit as you read the barcode, and barcode software will do this for you.

/2p (I've done a LOT of work on barcodes recently, although sadly it's been more converting part numbers to barcodes for printing, so the other way round!)
(Son of Sam-i-am We're all as mad as hatters here, Wed 4 Feb 2009, 11:47, Reply)