What is "SQ code"? Where can I find reference material for it?

[jonemo]

Support for a barcode symbology "SQ code" was added to zbar in 2019 in #2 by @jasp00. Can anyone share a link or other reference for where I can find out more about this 2D symbology? I am particularly interested in the official specification of the code as well as any licensing information related to its use.

What I was able to find so far:

I tried to find barcodes similar to the examples in zbar (1 and 2) in various online and printed references on barcodes and couldn't find anything visually similar. I also tried two commercial barcode decoding softwares with broad symbology support and they failed to decode the examples.

Web searches led me to 3, 4, and 5. Maybe there is something to be discovered there, but my lack of Italian language skills and the many dead links made me give up after some searching.

[jasp00]

Besides the decoding code in ZBar, I am virtually your only source about SQ code. Feel free to ask if you need more information, but please be patient, I may reply after a week.

SQ code is a patent-free technology. Barcode layout and wrapper format are public domain. I coded a wrapper and an encoder to XPM. These two programs are under GPLv3+, but they are simple; it would be easy to start from scratch in order to use a different license. I can share the source of these programs with you.

[jonemo]

Thank you for the reply! Do SQ codes exist "in the wild"? Are there places someone could go or documents to read where an SQ code would be found?

[jasp00]

No organization requires SQ code as far as I know. SQ code was designed to add printed digital signatures, so you could find such documents that were submitted to a governmental registry; I can show you examples of my documents. As a generic file container, you may find SQ codes in file transfers by paper, printed backups, and websites that only host images with lossy format.