Is it Perversion of Canon if her panties were visible, but not this visible, and not to the viewers?
Hmm this seems kind of like a tough one. It looked like Riko and You saw Chika's panties, so maybe you could count this as a freeze frame of their point of view? I think what the audience saw was an intentionally censored version of what the characters in the anime might have seen. Looking at it like that I don't think it's technically perversion of canon. I know that's mostly speculation on my part, but that's the way I look at it.
Is it Perversion of Canon if her panties were visible, but not this visible, and not to the viewers?
If it's naughtier than canon, even by an iota, then it belongs in the pool; regardless of how pervy the canon scene is and how pervy the fanart of that scene is.
A pic of Eleven saying "on their wedding night" with a Yaranaika face or even a very slight nosebleed would belong in the pool.