A whiteboard provides a large shared space for the participants to focus their attention and express their ideas, and is therefore a great collaboration tool for information workers. However, it has several limitations; notably, the contents on the whiteboard are hard to archive or share with people who are not present in the discussions. This paper presents our work in developing tools to facilitate collaboration on physical whiteboards by using a camera and a microphone. In particular, we have developed two systems: a whiteboard-camera system and a projector-whiteboard-camera system. The whiteboard-camera system allows a user to take notes of a whiteboard meeting when he/she wants or in an automatic way, to transmit the whiteboard content to remote participants in real time and in an efficient way, and to archive the whole whiteboard session for efficient post-viewing. The projector-whitebord-camera system incorporates a whiteboard into a projector-camera system. The whiteboard serves as the writing surface (input) as well as the projecting surface (output). Many applications of such a system inevitably require extracting handwritings from video images that contain both handwritings and the projected content. By analogy with echo cancellation in audio conferencing, we call this problem visual echo cancellation, and we describe one approach to accomplish the task. Our systems can be retrofit to any existing whiteboard. With the help of a camera and a microphone and optionally a projector, we are effectively bridging the physical and digital worlds.