Summary

So I found this plugin for SketchUp called Bitmap to Mesh and installed it to play with. After a few trials I mastered the technique and I'm now ready to go in schools to show 3D printing to kids. Black and White low rez pictures, croped and saved to BMP, 3 click operation in SketchUp and some customized writing and frame, saved to STL and printed in 5 minutes. For kids I'll print 4 at the time so it's quick and cost effective. They usually pay 300$ for a workshop like this in schools...
My suns' teacher wants to be first and then there are other teachers interested but then there are other schools, and lithophanes really have a magical effect on everyone.