Square Gear

I found this square gears at many places in the web but not at thingiverse. So my question was, how to design it in openscad. Basic input is a screenshot image, manipulated with gimp (or any other picture software).

first try was been to convert the image to dxf. Inkscape will do, but openscad didn't like to import this.

second try was to use a webservice for upload png and download dxf. I have found a lot of, but all of them request money. It is a very boring search because the credit card registration is at the end of the online design process of any website. (If you know a really free conversion service, please write in comment).

third try was, to import png to openscad. It will work only when size is highly reduced (picture < 256x256 pixel) and take very high rendering time (>15min). Outline of the object will be in pixels, so the printer will be unhappy about.

fourth try:

here you can watch the video of square gear I found
htt!ps://www.you!tube.com/watch?v=En7OFIyMD-c
(remove ! from the link)
and here is the download of a pdf
https://goo.gl/F0db5J

I've used this small and amazing software:

Openscad contour tracer
http://dpruimboom.magix.net/public/
htt!ps://www.you!tube.com/watch?v=QvL4TxJB4LU
whyever, it is forgotten in the world.
It is written for windows, but it runs in my linux system with no problems (if 'wine' is installed).
It gives a openscad script text to clipboard so it can be inserted in a text editor or directly.

then it was been easy to continue in openscad.
additional idea: openscad is able to export 2d elements as dxf. This combination will be annother kind of png to dxf converter.

License of this thing: My work is Public domain, because it is no invention and no new idea. Because of the unknown license of the imported data I will mark it as 'noncommercial'.

edit 2019-08-09
have found more instructions for inkscape:
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Using_the_2D_Subsystem#Rotate_Extrude
scroll to last paragraph.