Retinal Persistence

Also known as "Persistence of Vision", retinal persistence was the belief that when we see things, that the image is imprinted in our retina for a few hundred milliseconds, until it faded. The scientists at the time said that this is why when images are played one right after another, that this is what gives us the perception of motion. However, this theory was proven wrong on several different points.
 The first is that we actually still see movement , even with only 10 frames per second. That is to say that if you were to flip through 10 photos, they would still look like they were moving. This disproves that it stays in your retina for so long.
The second point, as seen on " The brain from top to bottom" is that if we were seeing images that lasted so long, then what we see should be images on top of each other on our retina. I kind of think of it like an opaque old image at the bottom of a new image of what we're seeing now.
All of this was proven wrong by Wertheimer in 1912.
The new theory that they have today is called the beta effect. It basically states that when two images that are only slightly different in appearance are played on after the other, that our brain automatically puts them together into believing that it's a moving image.
Pretty nifty stuff!

I know that people online have used this to their advantage to make cute or funny gifs, with just a couple images. For example a couple cute ones:

And even one I've made for my own blog! :

And some funny ones: