色々あるけど基本的にバックエンドはZBar，最近はQtqrをよく使っている．

• mchehab/zbar: ZBar is an open source software suite for reading bar codes from various sources, including webcams\. As its development stopped in 2012, I took the task of keeping it updated with the V4L2 API\. This is the main repository for it\. There's a clone at at LinuxTV\.org, and another one at gitlab\.

• Qreator in Launchpad

graphical utility for creating QR codes
 Qreator enables you to easily create your own QR codes to encode different
 types of information in an efficient, compact and cool way.
 .
 Qreator supports creating the following kinds of QR codes:
  - Business card
  - Geolocation
  - Phone call/SMS
  - Text
  - URL
  - Wi-Fi network

• libqrencode

QR Code encoder into PNG image
 Qrencode is a utility software using libqrencode to encode string data in
 a QR Code and save as a PNG or an EPS image.

$ qrencode
qrencode version 4.0.2
Copyright (C) 2006-2017 Kentaro Fukuchi
Usage: qrencode [OPTION]... [STRING]
Encode input data in a QR Code and save as a PNG or EPS image.

  -h           display this message.
  --help       display the usage of long options.
  -o FILENAME  write image to FILENAME. If '-' is specified, the result
               will be output to standard output. If -S is given, structured
               symbols are written to FILENAME-01.png, FILENAME-02.png, ...
               (suffix is removed from FILENAME, if specified)
  -r FILENAME  read input data from FILENAME.
  -s NUMBER    specify module size in dots (pixels). (default=3)
  -l {LMQH}    specify error correction level from L (lowest) to H (highest).
               (default=L)
  -v NUMBER    specify the minimum version of the symbol. (default=auto)
  -m NUMBER    specify the width of the margins. (default=4 (2 for Micro))
  -d NUMBER    specify the DPI of the generated PNG. (default=72)
  -t {PNG,PNG32,EPS,SVG,XPM,ANSI,ANSI256,ASCII,ASCIIi,UTF8,ANSIUTF8}
               specify the type of the generated image. (default=PNG)
  -S           make structured symbols. Version must be specified.
  -k           assume that the input text contains kanji (shift-jis).
  -c           encode lower-case alphabet characters in 8-bit mode. (default)
  -i           ignore case distinctions and use only upper-case characters.
  -8           encode entire data in 8-bit mode. -k, -c and -i will be ignored.
  -M           encode in a Micro QR Code.
  -V           display the version number and copyrights of the qrencode.
  [STRING]     input data. If it is not specified, data will be taken from
               standard input.

  Try "qrencode --help" for more options.
$ qrencode ほげ -o - | display
$ qrencode -l H -t ansiutf8 '😺'
█████████████████████████████
█████████████████████████████
████ ▄▄▄▄▄ █▀▄▄█ █ ▄▄▄▄▄ ████
████ █   █ █   ▀▄█ █   █ ████
████ █▄▄▄█ █ ▀█▀ █ █▄▄▄█ ████
████▄▄▄▄▄▄▄█▄▀ ▀▄█▄▄▄▄▄▄▄████
█████▀▄██▄▄ ▄▄▀ ▄▄█▄▄   █████
█████▄▄▀▀▀▄▀▄ █▄█ ▄█▀█▀▄█████
████████▄█▄▄▀▀█▀█  ▀██   ████
████ ▄▄▄▄▄ █ █ ████ ▄▄ ██████
████ █   █ ██▀ ▀█  ▄▄█▀█▄████
████ █▄▄▄█ █▄█▀█▄▀▀█▀▄█▄▄████
████▄▄▄▄▄▄▄████▄█▄▄██▄▄█▄████
█████████████████████████████
█████████████████████████████

ANSI,ANSI256,UTF8,ANSIUTF8 であれば端末に表示された物をそのまま読み込めた． ASCII,ASCIIi は加工向け?

• QR Tools in Launchpad

Qt frontend for QR code generator and decoder
 A Qt based software that help you to generate QR codes easily, scan
 an image file for QR codes and decode them or use your webcam to
 scan a printed one.

$ qtqr 
QPixmap::scaled: Pixmap is a null pixmap
libv4l2: error setting pixformat: Device or resource busy
libv4l2: error setting pixformat: Device or resource busy
libv4l2: error setting pixformat: Device or resource busy
libv4l2: error setting pixformat: Device or resource busy
WARNING: no compatible input to output format
...trying again with output disabled
libv4l2: error setting pixformat: Device or resource busy
libv4l2: error setting pixformat: Device or resource busy
Traceback (most recent call last):
  File "/usr/bin/qtqr", line 834, in decodeWebcam
    qr.decode_webcam(device=device)
  File "/usr/lib/python3/dist-packages/qrtools.py", line 240, in decode_webcam
    proc.init(device)
zbar.UnsupportedError: <zbar.Processor object at 0x7fc78602f180>
Aborted

• \#961503 \- qtqr: When you try to read the QR Code while using the camera, it crashes\. \- Debian Bug report logs

• NetworkManagerのWi\-Fi接続のQR code共有 \| edocr