Deadly Obsession by Carla Simpson

A clandestinely taken photograph of the daughter of one of London’s most prominent citizens sets Brodie and Mikaela off on a new case to find out who took the photograph of the now-missing girl.
When the family receives a second photograph of their daughter who is quite obviously dead, their simple inquiry becomes a murder investigation. But this is no routine investigation as another photograph is received, and another body found.
As more bodies turn up, and with no known motive, Brodie and Mikaela must confront the fact that the murderer is brilliant, disturbingly talented, and quite possibly insane. What drives this cold-blooded killer to capture the last moments of their victims with such haunting clarity?

Brodie has his own thoughts from years of experience with the Metropolitan Police, while Mikaela has an entirely different take on the murders.
Their inquiries take them from a struggling photographer who takes iconic photos around London then sells them for the stereopticons that have become so popular, to a casual photographer on the street with his box camera, and into galleries where photo exhibits are shown.