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 car