So, I actually researched this now..
The first image is "royalty-free".
The second image is "royalty-free", I found it on www.dreamstime.com.
I found the third image on google with free non-commercial and commercial use filter. Von Mises is on Wiki, so I think it is free to use.

I changed other images for which I was not sure. New images are free to use, some without, some with attribution.