I have found this excelent tool
Which does what I want, converting polygons, polylines and markers too. But it has a limitation. It generates URLs so big that the static maps API returns:
The remote server returned an error: (414) Request-URI Too Large.
I know that encoded polylines can be simplified until the URL be short enough to work. Is there any Web App which converts "My Map" to a simplified version of it using Static Maps? Is there any other Web App which could at least take an screenshot of Google Maps and generate an image for it?