Alternate views are treated the same way as the quick menu and the URM notifications by RenPy. When you use the "H" or click the mouse wheel to make the quick menu and URM notification disappear, it also makes the alternate view disappear, so you aren't able to get a "clean" screenshot of it. To do that, you have to disable the quick menu altogether (or have it so that it disappears if you aren't hovering it) AND, if you have URM installed (which you have to do to change the QM settings when the Dev didn't make hiding it a Main Menu option), you also have to disable URM's notification popups since trying to use "H" or the wheel click will also make the alternate render disappear as well.
Some folks don't mind having the detritus at the bottom; I don't like it and, if I want to get a clean shot of the alternate view, some method of hiding those things other than "H" or wheel click must be used. And, as I said in my first post, the other alternative is to Unren the images after the playthrough, but that can be a time consuming and space consuming process. What I'm doing now takes less time overall, but will kind of break the flow of the VN if you have to go in and turn everything off each time you see an alternate you want to save.