I can confirm what Spanakopita says, coming from a very horsey milieu myself.
The dressage rider was Charlotte Dujardin and she was previously a very, very successful rider (multiple golds at the Olympics and World Equestrian Games, winning against Germany whose top riders would normally have been expected to waltz off with the medals[. More to the point, Charlotte was held up as an example of how you can get to the top whilst respecting the horse. Well, she definitely respected her own horses (Valegro and his successor[ but not, by the looks of it, all of them.
Anyway, that's a bit of a distraction on my part from Spanakopita's point, and the point others have made, that all sports where animals are used will involve a degree of exploitation if not abuse - in the form of taking unecessary risks, very often. For me, polo ponies get the worst deal, with the mallets and hard balls but also with the tight turns, so hard on the joints, tendons and ligaments, and incredibly fast stop-start action, so hard on the heart. Polo ponies are closely followed in the hard-done-by stakes by national hunt racers, in my opinion... but that's if you were to wish to cut the data by discipline, whereas it may be fairer to say that there are some very caring owners and trainers, and some rather less so, in all of the disciplines. I used to think, for example, that dressage, my sport, was one of the kindest... that is, until the Charlotte Dujardin video surfaced.
As for "where are the pictures", it is well known in the horsey circles that the Drizzle affair played out just as Spanakopita says, and there are no "photos" that could prove that, as what you'd really need is a video of the groom audibly saying what he said to Harry, then Harry jumping on her for that last, fateful and fatal chukka. Which nobody has.
I don't condemn Harry any more than I condemn others who abuse animals... although I do think that since he had a string of ponies to choose from, insisting on riding Drizzle does seem particularly selfish. Maybe.