Most of the pictures on our Flickr account are now under a Creative Commons NonCommercial-Attribution-ShareAlike license. That means that from copyright viewpoint you can copy, remix & re-distribute the photos as long as it’s not for commercial purposes. They can for example used to illustrate blog posts
or Wikipedia articles. Just remember that if pictures have recognisable people you should respect their privacy.
The few pics that have all rights reserved are usually pics where the photographer has given us the right to use the images, but we haven’t yet asked them if it’s okay to let people remix the images.
Why? Why not. If Peter from Northampton needs a picture of a Koala for his school presentation of animals that fail in natural selection then why not let him use the one Janos took? It’s not like we’re loosing anything. But maybe koalas win if Peter’s presentation is a bit more convincing and gets Mary to study to be a vet whose research saves those cute, fuzzy bears from extiction. Probably not though.