Photosynth is a Microsoft technology that analyzes digital photographs and generates a 3D model and point cloud by identifying common points between images, allowing users to virtually tour spaces by walking or flying through generated scenes and zooming in on details. It works by analyzing multiple photographs through interest point detection and bundle adjustment to determine angle, distance, and 3D position information to accurately replicate environments like buildings, with the best results coming from taking photos every 15 degrees when turning corners or from wider angles of interior spaces.