So if a photograph with people on the street is cropped to show only one person, then the person is isolated and can sue for the photo to have been taken? But this could be any photograph with sufficiently high technical quality. The "isolation" can be done in post. Personally this doesn't make any sense as when the person is isolated, it tells less about what they were doing, where they were, and things that could violate their privacy than a photograph where the person is e.g. talking with someone they don't want to be seen talking with. A close up (showing either just face, the body or something in between) just shows how they looked on that day nothing revealing or damning. I don't understand why someone would find that reason to sue: their secret lover (or the politician who colludes with them on something not publicly known) is outside of the picture. An isolated image tells less than an image showing a person in an environment, interacting with others.
The case you need to look up in this connection is between the photographer Francois-Marie Banier and Isabelle de Chastenet de Puysegur. Banier published a book called Perdre la Tete, in which photographs of marginalised - often homeless and/or mentally ill - people were juxtaposed with photographs of famous or not famous but very definitely not marginalised people. Mme de Chastenet, who is every bit as magnificent as her name, was one of the latter. She was photographed sitting on a park bench, elegantly dressed, with her dog. She was definitely the subject of the photograph, and turned toward the camera so she was clearly identifiable. There was no caption or text associated with the photograph - the court specifically noted this in the judgement. She made three claims: that she had objected when she realised she was being photographed, that a woman sitting on a park bench is not an
actualite - a public event at which one can expect to be photographed - and that the juxtaposition made her appear to be a rich woman indifferent to the sufferings of the marginalised. The court did not believe the first claim, with regard to the second said that Banier was making a coherent statement about, if not actually news, the state of the world, which was close enough to
actualite, and with regard to the third said exactly what you said: the photograph showed an elegant woman sitting in the park with her dog.
However, the editor and owner of the magazine which published the covertly taken photographs of Prince William and Kate Middleton tried to make exactly the same argument: all they showed was that she looked very nice with her top off, and it didn't work for them: they were convicted and fined the maximum 45,000 euros each.
They can't sue because it has been taken
unless they object at the time and it is taken anyway, but they can sue if it is
published without consent,
except for news reporting, artistic creation, etc,
unless it is demeaning or seriously offensive to the person shown. But you are perfectly right that if it is simply a portrait the damages are likely to be minimal at most. Even Kate Middleton, who was in a private place when she was photographed and was shown partially nude, only got 100,000 euros in damages.