It may be the point where the photographer is first made aware of the restriction but it definitely is not the point where the restriction is in place.
When on 'Private' land it is the responsibility of the photographer (or anyone else) to familiarise themselves with the conditions for access, similarly to establish whether or not they are on 'Private' or 'Public' land.
There is NO law at all against taking photographs on private land either statutory or civil.(There are moves to make trespass on land a criminal offence)
The only law that can be invoked on a photographer ON private land is that civil tort of trespass by way of physically being on the land. Nothing to do with the fact he maybe taking photos.
The land owner does NOT have to communicate it is private land for a claim of trespass on the land. The land owner can seek damages or/and he can use reasonable force to move a person from the land. "per se" (by right)
If signs are put up on private land or it is communicated, stating NO photography, a civil case may be possible against the photographer providing damages can be quantified by the plaintiff(land owner) for the taking of those photos.
If the land owner has not communicated that he does not want photos taking on his land there can be be no claim against the photographer, as there has been no instruction from the land owner preventing photography.
A person who owns land does NOT have any legal right preventing photography on his land 'per se"(by right). That means there is no law made by anyone, anywhere saying " if you own land a person who is on your land needs your permission to take photos and if they do not seek out and obtain your permission you can sue for damages". No law at all.
There has to be some form of contract established between the land owner and the photographer for the photographer to be in breach of the conditions of entry.
Silence by the land owner is not an option.
If the land owner allows the person on to their land, the land owner needs to say in some way "no photographs can be taken" otherwis photos can be taken. The onus is always on the land owner to make the restrictions known.
The land owner cannot sue for taking photos as per se(by right) like he can for trespass onto the land. IE he needs to make the photographer aware of what the rules are.
Laws are made by Parliament or the courts. Not land owners. Land owners have to make a contract. IE if you enter onto this property you cannot take photos.