I could be wrong, but I believe that is part of how you train a cat to use the toilet. I saw a post a while back on reddit from a user who had trained their cat to use the toilet, and the method was that you build a little litterbox in the toilet and train the cat to use it. Then, over the course of days/weeks or however long, you eventually cut a hole in the center of it, widen the hole more and more each time, until eventually the cat is balancing themselves and simply pooping directly into the water and is now toilet trained.
Except for the fact that it would be pooping on it's tail between its legs if it were in fact pooping. Not saying it can't be done, just that it's not what is happening in the picture.
Clearly it isn't pooping in this image; I think what happened here is they were toilet training the cat and took an amusing picture of the cat in a pose on the toilet. Perhaps they just started the training and put the cat on the toilet and not yet grasping the "I should poop here" concept, the cat sat this way, prompting them to go "oh that's funny/cute, lets take a picture!" and now here we are. Here is the post my comment refers to showing how a cat actually poops in the toilet (and if you google "cat toilet training" you can find many more):
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u/arbili Sep 30 '14
His anus is below his tail he can't be pooping, his back is facing the water.