Visual surveillance systems are increasingly common in our society today. There is a conflict between the demands for security of the public and the demands to preserve the personal integrity. This thesis suggests a solution in which parts of the surveillance images are covered in order to conceal the identities of persons appearing in video, but not their actions or activities. The covered parts could be encrypted and unlocked only by the police or another legal authority in case of a crime. This thesis implements a proof-of-concept demonstrator using a combination of image processing techniques such as foreground segmentation, mathematical morphology, geometric camera calibration and region tracking. The demonstrator is capable of tracking a moderate number of moving objects and conceal their identity by replacing them with a mask or a blurred image. Functionality for replaying recorded data and unlocking individual persons are included. The concept demonstrator shows the chain from concealing the identities of persons to unlocking only a single person on recorded data. Evaluation on a publicly available dataset shows overall good performance.