An information processing system comprising: a first information processing apparatus and a second information processing apparatus, the first and second information processing apparatus (30A, 30B) being connected to each other via a network, the first and second information processing apparatus (30A, 30B) being configured to receive, upon their respective request, image data of an object image from an image server; the first information processing apparatus being configured to display a first image in a first window on the basis of the received image data, the first window having an operation right for a user of the first information processing apparatus with respect to the first image displayed in the first window, an operation right referring to a right to perform an operation including move, zoom factor changes and/or rotations; and the second information processing apparatus being configured to display a second image in a second window on the basis of received image data of the same object image, the second information processing apparatus having a synchronous state, in which an operation, instructed by a second user of the second information processing apparatus with respect to the second image displayed in the second window is disabled, and the second image is the same image as the first image, the same image relating to the same object image's area in the same zoom factor and the same angle, and the second information processing apparatus further having an asynchronous state, in which the second image is a result of arbitrary operations by a user of the second information processing apparatus relating to received image data of the same object image, such that the second image may differ from the first image; the second information processing apparatus being further configured to: (a) in response to a first request by a user of the second information processing apparatus, switch from the synchronous state to the asynchronous state; and (b) in response to a second request by a user of the second information processing apparatus, switch from the asynchronous state to the synchronous state. a first information processing apparatus and a second information processing apparatus, the first and second information processing apparatus (30A, 30B) being connected to each other via a network, the first and second information processing apparatus (30A, 30B) being configured to receive, upon their respective request, image data of an object image from an image server; the first information processing apparatus being configured to display a first image in a first window on the basis of the received image data, the first window having an operation right for a user of the first information processing apparatus with respect to the first image displayed in the first window, an operation right referring to a right to perform an operation including move, zoom factor changes and/or rotations; and the second information processing apparatus being configured to display a second image in a second window on the basis of received image data of the same object image, the second information processing apparatus having a synchronous state, in which an operation, instructed by a second user of the second information processing apparatus with respect to the second image displayed in the second window is disabled, and the second image is the same image as the first image, the same image relating to the same object image's area in the same zoom factor and the same angle, and the second information processing apparatus further having an asynchronous state, in which the second image is a result of arbitrary operations by a user of the second information processing apparatus relating to received image data of the same object image, such that the second image may differ from the first image; the second information processing apparatus being further configured to: (a) in response to a first request by a user of the second information processing apparatus, switch from the synchronous state to the asynchronous state; and (b) in response to a second request by a user of the second information processing apparatus, switch from the asynchronous state to the synchronous state. (a) in response to a first request by a user of the second information processing apparatus, switch from the synchronous state to the asynchronous state; and (b) in response to a second request by a user of the second information processing apparatus, switch from the asynchronous state to the synchronous state.