Keyes, John (22 August 2003). "KarTrak". John Keyes Boston photoblogger. Images from Boston, New England, and beyond. John Keyes. Archived from the original on 10 March 2014. Retrieved 26 May 2013.
Rawsthorn, Alice (23 February 2010). "Scan Artists". The New York Times. ISSN0362-4331. Archived from the original on 18 November 2016. Retrieved 12 February 2026.
Oberfield, Craig. "QNotes Barcode System". US Patented #5296688. Quick Notes Inc. Archived from the original on 31 December 2012. Retrieved 15 December 2012.
Keyes, John (22 August 2003). "KarTrak". John Keyes Boston photoblogger. Images from Boston, New England, and beyond. John Keyes. Archived from the original on 10 March 2014. Retrieved 26 May 2013.
Rawsthorn, Alice (23 February 2010). "Scan Artists". The New York Times. ISSN0362-4331. Archived from the original on 18 November 2016. Retrieved 12 February 2026.
Oberfield, Craig. "QNotes Barcode System". US Patented #5296688. Quick Notes Inc. Archived from the original on 31 December 2012. Retrieved 15 December 2012.
Rawsthorn, Alice (23 February 2010). "Scan Artists". The New York Times. ISSN0362-4331. Archived from the original on 18 November 2016. Retrieved 12 February 2026.