Until now, two of the slides had images that were taken from the
Nature magazine. However, Nature does not allow redistribution of its
images! Therefore, by presenting its images in presentations and
sharing the PDF here, we were violating its copyright.

With this commit, the two images have been deleted and their slides
have been adjusted to have links to the respective paper for easy
clicking during a presentation (and showing them from Nature's own
webpage).

This issue was raised by Boud Roukema.

Until now, for the image showing a binary data analysis we were using
an image without a clear copyright statement.

In this commit, that image has been replaced by one from Wikipedia
Commans that has a sharable copyright notice.