As an example, the fake news about the guy that found the warehouse full of fake ballot boxes for Clinton:

A Google Image Search of the picture in the fake article would have found the picture is much older, and isn't what the caption described.

If I'm tech-savvy and skeptical, I might have done that when consuming the article, and decided on my own it was fake. Machines can do that automatically for people that aren't tech-savvy, or that don't start reading it with a skeptical mindset.