A view days back I found again a plugin here on hackaday.io, the "Raster 2 Laser GCode generator". It is a plugin for Inkscape to generate Gcode from images files like jpg, svg and png in different styles for laser engraving !

I testet it with some QRcode-images, and here are the results:

I engraved them on very thick and dense cupboard:

From left to right (1: 50 x 50 mm, 5 px / mm, S100, F200; 2: 30 x 30 mm, 2 px / mm, S100, F250; 3: 30 x 30 mm, 5 px / mm, S100, F250; 3)

As you can see, the 5 px / mm setting results in nice dark blocks. The lower setting on the other hand gives visible spaces in the dark blocks. This QRcode could not be read by my smart phone. The other two work nicely.

In the next tests I will attempt to make tiny (10 x 10 mm) codes on cupboard or wood...