People think that things like cameras and radar are perfect instruments. They can be overloaded by things like pointing them at the sun, internal reflections, radar can have false signals, etc. I once thought I saw a UFO while in a car and then realized it was just an internal reflection of a light off of the glass. It looked like it was moving super fast and everything.
People will also do things like over expand compressed videos and images and then act surprised when they see compression artifacts and think they are real.