Image control involves receiving source images defined with respect to respective source coordinate systems from source image generators also respectively associated with source IDs. The source images are composed to generate a composite image defined with respect to a composed coordinate system, and the composed image is sent to a viewer which displays the composed image and outputs an HID signal which indicates information defined with respect to the composed coordinate system. A layout manager stores source IDs respectively associated with layout information including position and size of at least one of the source images. An image composer composes the source images according to the layout information. An analyzer analyzes the HID signal for editing layout information stored in the layout manager, and determines a source ID a source image according to the layout information. The HID signal defined with respect to the composed coordinate system is converted to an HID signal defined with respect to the source coordinate system corresponding to the determined source image. An operator then sends the converted HID signal to the source image generator associated with the determined source ID.