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=En7OFIyM