The pictures are completely free to be used for any legal purposes.
The pictures are free for personal and even for commercial use.
You can modify, copy and distribute the photos.
All without asking for permission or setting a link to the source. So that attribution is not required (but if you do, I would be very grateful).
The only restriction is that identifiable people may not appear in a bad light or in a way that they may find offensive, unless they give their consent.