Actually it looks like it's just wearing a halter. I think what looks like another piece of tack is just coloration.

In any case this is not abuse (is he a troll or just ignorant?). I've rarely had trouble getting a halter on a horse except for one who doesn't like his ears being touched. My take is that if an animal that's basically 1,100 lbs of muscle (OK,not that one :-) lets you do something, it's not too bothered by it! Horses have absolutely no problem letting you know when they're pissed.

How would you like it if I put a bridle on your face.

Animals are not people.

I'm completely with you, but this is not the right place for this discussion. Lead by example (adopt a 100% cruelty-free lifestyle) and let your influence slowly trickle out through your social network.

I'm not so concerned about the issue that I am willing to agitate on a tech forum, but when I see this I feel bodily distress.

I am not so pleased to see an argument for the banality of evil on what is normally a bastion of liberal hipster moral righteousness either.

Well, now we're talking in terms of relativity. You're saying that it's not 'horrible abuse' because it is standard treatment, but this says nothing of whether or not standard treatment is 'horrible abuse.' For example,

   The Jews that weren't killed in the concentration camps "didn't have
  it so  bad" compared to the ones were. But this says nothing of whether
    or not overall treatment of Jews in concentration camps was good or bad.

I'm saying that it's not "horrible abuse" because:

a) I've spent a reasonable amount of time around horses;

b) Can see nothing in that photo to suggest the horse has been mistreated or is distressed; and

c) Find this kind of trivialization of animal abuse by someone who has little experience with horses to be offensive nonsense.

There's real "horrible abuse" out there, and this is most emphatically not an example of it.

Whoa, I never expected Godwin to show up in a discussion thread about a horse.

Godwin's law only applies when calling someone a Nazi or comparing someone to a Nazi(s). Godwin doesn't cover the word 'Nazi' or 'Jew' turning up in a discussion.