interactive whiteboard-Front and rear projection

Interactive whiteboards are generally available in two forms: front projection and rear projection.

Front-projection interactive whiteboards have a video projector in front of the whiteboard. A disadvantage of front-projection whiteboards is that the presenter, standing in front of the screen, must extend his or her arm with or without a stylus to avoid casting a shadow. This is not a disadvantage of Ultra-Short-Throw (UST) projectors, which cast an image from above and just in front of the IWB surface, removing the presenter from the beam's path.

Rear-projection interactive whiteboards locate the projector or emmisive display behind the whiteboard sensing surface so that no shadows occur. This also avoids the problem with front-projection boards that the presenter has to look into the projector light while speaking to the audience. However, rear-projection systems are generally significantly more expensive than front-projection boards, are often very large, and cannot be mounted flush on a wall, although in-wall installations are possible.
Some manufacturers also provide an option to raise and lower the display to accommodate users of different heights.