I don't think its so much that they fall for it but that people create fake images that confirm what people already believe and the viewers deeply want the image to be true and will not think critically.
Verifying an image is not impossible. You just have to consider:
* Who took the image
* Do they have any reasons for wanting to fake it?
* Was anyone else able to verify they saw or took a photo of the same thing
* Is anyone in disagreement with the content of the image
We don't need image manipulation to fool people on facebook. Recently a random image of a park full of rubbish was used with the caption that this was the result of a recent environmental protest but the image was actually months old from a totally unrelated event. People believed and shared it because they wanted to. You could just as easily write a text post saying you saw a bunch of rubbish after the event and you would have almost the same effect.
Wait. No. I had that backward.
How long has photo manipulation been around? And people still fall for it every minute of every day.
I have zero faith these tech developments will lead to anything good, or that we'll even learn how to deal with them effectively.