Licensing of the images

The license at `privacy-protocols/LICENSE.md` says:

> This repository, along with any additional material in this repository (images, presentations, etc.) is available for use with attribution under the Creative Commons Attribution 4.0 International (CC BY 4.0) license.

However, I'm not sure you have the rights to license all the images (in `privacy-protocols/images/`) under a CC BY 4.0 license. Do you?

You do if you created all the images (and hold the copyright), or they are already licensed CC BY 4.0 or similar. If so, then this is a non-issue and it can be closed.

If you can't license the images CC BY 4.0, then you should:

* Edit `privacy-protocols/LICENSE.md` to say that it only covers the text and the images that you _can_ license (listed), but _not_ the other images.
* When an image is used in `README.md`, include a caption giving appropriate credit to the source.

P.S. The cat image doesn't seem to be used in `README.md`. It it an Easter egg?

Assigning to @vrde