There are quite a few hacks around but I wondered if there was some reason these aren't more widespread or commercially available. Business idea? You could als

There are quite a few hacks around but I wondered if there was some reason these aren't more widespread or commercially available. Business idea? You could also make something that filters all light but near infra-red so it could be seen by CCDs (on cameras or phones) but not with the human eye. Or do the reverse and flood the picture with near infra-red to prevent it being photographed.