Ask YC: Reconstruction of Data from a Chart or Graph

I have here several charts of driving cycles. These are standard plots derived from real traffic data, of velocity versus time. Unfortunately I cannot find the data anywhere. So I hatched a plan: maybe there's software that will reconstruct data from a graph or chart? Does anyone know?

If not, I'll just write it myself and open source it. It seems like a generally useful thing in engineering and science. It deserves an application (maybe even a web application).

A picture of the drivecycle is here: http://einfall.wordpress.com/2008/10/26/reconstruction-of-data-from-a-chart-or-graph/