A monitoring camera system comprising: image obtaining means (101, 102) for obtaining a sequence of captured images in a time series; analysis means for generating metadata, recorded in correspondence with a captured image of the sequence of captured images, by performing object detection on the captured image, the metadata including position information indicating a position of each object in the captured image, an attribute of each object as a result of the object detection, and, for each object, flag information indicating whether said respective object present in the captured image is a masking target; wherein the masking target is an object in the captured image, which is to be anonymized, wherein the analysis means is configured to set a value of the flag information to a default value or to set said value of the flag information in accordance with the attribute of the object, wherein the analysis means is configured to set the flag information for each user who is to view the captured image, for each user group of the user who is to view the captured image, for each image display apparatus which is to display the captured image, or for each installation location of the image display apparatus which is to display the captured image, and wherein said value of the flag information is changeable by user designation; and mask processing means (405, 406, 407) for generating an image in which an object, among the objects detected from the captured image, which is indicated as the masking target by the flag information, is masked, wherein the mask processing means (405, 406, 407) comprises generating means for generating a background image based on the sequence of captured images, wherein in the background image a masking target object being indicated as the masking target by the flag information is not present, and combining means for combining the background image with an image in which mask processing has been performed on the masking target object, and wherein the combining means generates a protection image by masking a masking-target object region, which is determined based on a difference image between the captured image and the background image, and combines the protection image and the background image. image obtaining means (101, 102) for obtaining a sequence of captured images in a time series; analysis means for generating metadata, recorded in correspondence with a captured image of the sequence of captured images, by performing object detection on the captured image, the metadata including position information indicating a position of each object in the captured image, an attribute of each object as a result of the object detection, and, for each object, flag information indicating whether said respective object present in the captured image is a masking target; wherein the masking target is an object in the captured image, which is to be anonymized, wherein the analysis means is configured to set a value of the flag information to a default value or to set said value of the flag information in accordance with the attribute of the object, wherein the analysis means is configured to set the flag information for each user who is to view the captured image, for each user group of the user who is to view the captured image, for each image display apparatus which is to display the captured image, or for each installation location of the image display apparatus which is to display the captured image, and wherein said value of the flag information is changeable by user designation; and mask processing means (405, 406, 407) for generating an image in which an object, among the objects detected from the captured image, which is indicated as the masking target by the flag information, is masked, wherein the mask processing means (405, 406, 407) comprises generating means for generating a background image based on the sequence of captured images, wherein in the background image a masking target object being indicated as the masking target by the flag information is not present, and combining means for combining the background image with an image in which mask processing has been performed on the masking target object, and generating means for generating a background image based on the sequence of captured images, wherein in the background image a masking target object being indicated as the masking target by the flag information is not present, and combining means for combining the background image with an image in which mask processing has been performed on the masking target object, and wherein the combining means generates a protection image by masking a masking-target object region, which is determined based on a difference image between the captured image and the background image, and combines the protection image and the background image.