A system in which multiple computers engage in a collaborative video conference. One computer generates a common image which is distributed to the other computers. The invention allows the users of the other computers to annotate (that is, mark up, by drawings and text) the image at their respective computers. The invention replicates the annotations at the other computers.
One type of annotation allowed is "highlighting," wherein a user drags a cursor across a display, and the invention leaves a colored trail behind the cursor, which is transparent, and does not obscure the underlying images.