I've tried to make Analog Lenticular Animation before and it's just too tedious for me. I haven't the equipment nor the patience for it. There are a number of 'how-to' videos on the subject already. Here's a playlist of those types of videos compiled by another creator, ru-vid.com/group/PLFj10AAghnXiGcZ7UvsseFdjbzchZvITA.
Yes, you can do a rectangle shaped picture. Check out this playlist of the other videos I've posted using the changing pictures/blinds mechanism ru-vid.com/group/PLW8hSlX48si6MsDrkYvM8kMBXgBIDdR_k. I made one with an oval frame and one with a rectangular picture. If you watch them all you'll see that the mechanism can be applied to most size photos.