Find corners of pages

For the eye-tracking project of Jacolien van Rij we want to stabily localize pages recorded by the eye-tracking glasses, in order to determine what a child is looking at on a page.

[This notebook](notebooks/Example%2C find corners via circles.ipynb) illustrates the process and [this notebook](notebooks/Finding page corners for several images.ipynb) shows the result for several (2) example images.