A computer implemented method of privacy masking video surveillance data is provided, wherein the video surveillance data includes metadata associated with video data, the metadata describing objects or activity in the video data. A location of each item of metadata within its respective frame is compared with privacy mask data defining a position of a privacy mask in the frame; and based on the comparison, it is determined if the metadata is to be masked. The item of metadata is masked if it is determined that the item of metadata is to be masked.