Most of them are not what they seem
CCTV footage of ghosts. Or maybe I should say "ghosts," because most of these things are obviously anything but.
It seems like every day, a little bit more of the world is covered by CCTV security cameras. These systems monitor our public and private spaces 24/7, which means there is a lot of potential for catching paranormal phenomena. (Assuming that whoever is monitoring the cameras bothers to look, of course!) Unfortunately, several weaknesses inherent in the system make it also likely that a lot of false positives will be filmed… and it seems like they all end up on YouTube at one point or another.
This is an obvious problem. Let's say you're bored, creative, and have access to someone else's security camera. Maybe it's pointing at a neighbor's driveway, maybe it's filming the parking lot across the street. Maybe it's at your workplace, either current or former.
Eventually, you might start to get the itch to play a little joke. There are a lot of ways you can prank someone on the other end of a security camera. Remote control vehicles, puppets, kites, and models being pulled across the camera's vision on fishing line all come to mind.
Security cameras have a fixed depth of field which is designed to keep their subject - usually at least 20 feet away - in focus. If a bug lands on the lens, most of them can't refocus on the insect. Instead, you end up with a big blur which moves around on its own.
To make things worse, many security cameras have IR lights, which can attract insects. And many insects have shiny or light-colored bodies which reflect the light in weird ways.
3. Poor Resolution
If you move too quickly, many security cameras will capture only a blur of motion. You could probably dress up in a sheet and run past most CCTV cameras after dark, and it would look pretty eerie on tape.
From a forensic perspective, this poor resolution means that it's impossible to really dissect what you are seeing. Congratulations: you caught a blob on camera. All anyone can tell is "it's a blob." It could be an angel, a ghost, or just a headlight reflecting off a nearby window at a strange angle.
The correlation is, it's pretty easy to gin up a hoax on CCTV footage. You don't need much technical sophistication to make an alien seem to appear on security camera tape!