Can they do that?

"Photography, filming and painting for commercial purposes is not permitted on The Estate without our express consent." There's a big sign (that most people don't seem to notice - my husband didn't see it, anyhow) as you go down to Lulworth Cove, saying pretty much what I've quoted from the Lulworth estate Web site, above. Except it doesn't emphasise the "for commercial purposes" bit as much. I wonder if they are really allowed to do that. Even if they are - on their own land - there's a public footpath running through the cove, and the beach below high tide belongs to the crown, so the waters are, so to speak, muddy. Anyway, I made a sketch regardless. It's not for commercial purposes, right?