![](http://photos1.blogger.com/blogger/353/70/320/timescope.jpg)
These guys augmented a telescope to overlay historic (or futuristic) images of a landscape the 'scope is trained on. "The basic idea of the "timescope" is a virtual journey in time via telescope. The device contains additional controls that enable viewers to view a place in the past or future time through its eyepiece." I imagine you can embed virtual billboards, too.