We already have a great barcode generator, but it would be good to have a barcode reader.
ZBar is a great software, it can read a barcode from a picture or camera. It is "an open source software suite for reading bar codes from various sources, such as video streams, image files and raw intensity sensors. It supports many popular symbologies (types of bar codes) including EAN-13/UPC-A, UPC-E, EAN-8, Code 128, Code 39, Interleaved 2 of 5 and QR Code."
PS: There's a topic about qrDecoder. Unfortunatelly, qrDecoder can't read barcodes from a camera.