Menachem:
It’s going to pretty much be guaranteed to happen in any Chabad that’s a house-shul like I mentioned. Admittedly, I don’t know that I’ve seen it in an actual beis medrash, but I wouldn’t have really noticed it. I’ve never jumped to the assumption that anyone’s kavana was to bow down to the picture as a replacement for Hashem; Chabad just likes putting Rebbe pictures everywhere. Seems like a strange thing for either side of this conversation to make a big deal of.
To everyone else:
You’ve gotten the Lubavitchers either on this thread or elsewhere to admit that they believe the Rebbe is/will be moshiach. You’ve gotten them to admit that they don’t see anything theologically wrong with someone believing the Rebbe is literally alive and sitting in the empty chair in 770. What more are you looking for? If the neutral parties reading this thread still have no objections to Chabad even with those things out in the open, then they never will, no matter how many Litvish gedolim you bring in who say they should.