Convert PNG to CNC-Ready STL

I need a PNG image converted to an STL file suitable for CNC routing. The final piece will be large, using foam as the material. I converted a photo of a fireplace surround to an STL file and tried to have someone route it in foam but the file came out with way too much detail so it wouldn't look right. I'm looking to have someone here make the fireplace surround out of foam.

Requirements:
- Convert detailed PNG images to STL files
- Ensure compatibility with CNC routing
- Handle large dimensions (over 60cm in any dimension)
- Experience with 3D modeling software and CNC processes