A system (102, 500) comprising: a processor; and a non-transitory storage medium (504, 600) storing instructions executable on the processor to: receive information sensed by an optical sensor (116, 310) responsive to light from a plurality of markers (118, 308) arranged to indicate respective different locations of a boundary of a physical user collaborative area (120, 306) to receive user-input marks during a video conference session; determine, based on the received information, the boundary of the physical user collaborative area (120, 306); and control, based on the determined boundary, a video zoom into the physical user collaborative area (120, 306) during the video conference session; characterized in that: the plurality of markers (118, 308) are distinct from the physical user collaborative area (120, 306); and the plurality of markers (118, 308) comprise a plurality of light emitters, and the received information corresponds to light emitted from the plurality of light emitters as sensed by the optical sensor (116, 310). a processor; and a non-transitory storage medium (504, 600) storing instructions executable on the processor to: receive information sensed by an optical sensor (116, 310) responsive to light from a plurality of markers (118, 308) arranged to indicate respective different locations of a boundary of a physical user collaborative area (120, 306) to receive user-input marks during a video conference session; determine, based on the received information, the boundary of the physical user collaborative area (120, 306); and control, based on the determined boundary, a video zoom into the physical user collaborative area (120, 306) during the video conference session; characterized in that: the plurality of markers (118, 308) are distinct from the physical user collaborative area (120, 306); and the plurality of markers (118, 308) comprise a plurality of light emitters, and the received information corresponds to light emitted from the plurality of light emitters as sensed by the optical sensor (116, 310). receive information sensed by an optical sensor (116, 310) responsive to light from a plurality of markers (118, 308) arranged to indicate respective different locations of a boundary of a physical user collaborative area (120, 306) to receive user-input marks during a video conference session; determine, based on the received information, the boundary of the physical user collaborative area (120, 306); and control, based on the determined boundary, a video zoom into the physical user collaborative area (120, 306) during the video conference session; characterized in that: the plurality of markers (118, 308) are distinct from the physical user collaborative area (120, 306); and the plurality of markers (118, 308) comprise a plurality of light emitters, and the received information corresponds to light emitted from the plurality of light emitters as sensed by the optical sensor (116, 310). the plurality of markers (118, 308) are distinct from the physical user collaborative area (120, 306); and the plurality of markers (118, 308) comprise a plurality of light emitters, and the received information corresponds to light emitted from the plurality of light emitters as sensed by the optical sensor (116, 310).