In some examples, a projector is controlled to project an image content onto a projection surface in a region defining a display area. Captured images are received that are captured by at least one optical sensor of the projected image content on the projection surface. In the captured images, user touches of a plurality of designated locations of the projected image content on the projection surface are detected. A position of an interaction area based on the detected user touches is determined, and, based on the determined position of the interaction area, it is determined whether the display area and the interaction area coincide.