Animage says that it makes illusion spells work on higher level animals, while Kindred Mage says it makes illusion spells work on higher level people.

However, if I go here, I see a listing of all creatures in the game by category:

http://www.uesp.net/wiki/Skyrim:Creatures

Animals seems to only entail a bunch of weak stuff (as well as wolves, mammoths, bears, and sabre cats). Meanwhile, A LOT of the stuff you will fight are listed as monsters, undead, automatons, and daedra. Those are not animals, but it seems unlikely that they are "people," so the kindred mage perk won't work either. Is this true?

If so, I think this really limits the effectiveness of illusion spells, as you're missing a huge level boost to your spells against most enemies.

I believe that any enemy that isn't affected by those perks is the type of enemy that's immune to Illusion spells in the first place (without the final perk).

Hmm. But " monsters" such as falmer, spriggans, giants, trolls, spiders, ice wraiths, etc (ie. a lot of enemies) are affected by illusion spells in the first place, but I'm not sure that they are considered either "animals" or "people."

Not sure about giants, but everything else you listed definitely gets affected.

It "gets affected" as in those perks work on them, or just that illusion magic works in general on them?