p.1 #1 · Licensing, Model release for educational purposes
Are you required to get model release forms if the photograph will be published for educational purposes? In a book? Does it differ depending on the country of publication?
p.1 #2 · Licensing, Model release for educational purposes
Probably, yes and yes.
If you intend to sell the book in the US then you'll want model releases. Copyright varies in other countries but for a commercial work, I'd expect you'll need the releases in most countries.
p.1 #3 · Licensing, Model release for educational purposes
In the US, probably no, probably irrelevant, yes. To expand, does the use in an educational setting infringe any of the individual's rights? Assuming no untoward circumstances in the taking of the picture, the content or context and not infringing say medical privacy, etc., there's no need for a release for what should be "educational" uses. Not sure why publishing in a book would be different from any other sorts of publishing. Laws can vary from country to country (and state to state when it comes to privacy and the like). Not a copyright issue.
p.1 #5 · Licensing, Model release for educational purposes
If it's for a book, it's usually editorial, educational or not. Be aware though that used in marketing material for a book (or magazine), things may get more complicated.