Film the Hand

When someone really doesn't want to be filmed, they'll stick their hand in front of or over the lens.

For someone filming hands doing something, that's An Insert. Or Hand of Death.

When someone accidentally blocks the lens with their own hand, that's Camera Obscurer.

Film

 * The end of Monty Python and the Holy Grail.
 * Wendy does this when Ben tries to film their breakup in the pilot of The Middleman.
 * In Frank Miller's version of RoboCop, a robber being caught on a TV camera punches the camera in order to keep from being filmed.
 * In at least two of Michael Moore's movies, several people he's trying to interview- up to and including senators- don't even let his camera get close enough to put their hand over it. Some of them actually break into dead runs upon seeing him on the opposite side of the street.
 * In The Dark Knight, Lao is telecommuting to the meeting of Gotham's crime bosses. The Joker interrupts the meeting and verbally tears into Lao, at which point he puts a hand over the lens and the connection cuts off.
 * In the first Shrek movie, just before Shrek and Fiona can have their wedding kiss, Shrek covers the camera.
 * Verne does this twice in the bonus short "Hammy's Boomerang" on the DVD of Over the Hedge, both times involving RJ and his lackies attempting to make fun of someone (either Hammy or him) on camera.
 * Occurs in Die Hard 2, when an overzealous reporter tries to question Colonel Stewart, his crony covers the camera and says "No pictures, you pinko bitch."
 * In Live Free Or Die Hard, McLane puts his hand over Warlock's webcam when the Big Bad hijacks it to talk to them, and asks Warlock if he can trace it. The Big Bad has to point out that covering up the camera does not shut off the microphone.
 * In the 1920 Buster Keaton short film One Week there's a scene with Sybil Seely (who plays his wife) taking a bath. When she leans out of the tub to retrieve the soap, a hand is placed over the lens.

Literature

 * Sunshine does this in Robin McKinley's book Sunshine to avoid being filmed by an overly zealous reporter in the middle of trying to make things go back to normal...
 * She also wasn't sure whether or not vampires would be watching the broadcast.

Live Action Television

 * Without a Trace, where the person being filmed ends up knocking the camera to the ground.
 * Scully does this at least once in The X-Files episode "X-Cops" (she really hates the camera guys and is very direct about informing them of this).
 * Every "fraud against consumers" style TV show tries to have those as often as possible, it gives a visual "proof" that whoever has just been explained to be a con artist is not even bothering to claim innocence. Smarter scammers set up rendezvous and don't show up which robs the show of the intensity this visual trope provides; thus fooling most consumers on how which fraud artists are skilled career criminals and which are amateurs.
 * Blon does this in the Doctor Who episode "Boom Town".
 * Detective Chief Inspector Gene Hunt does this to a newspaper photographer. This becomes a (very) minor plot point later on, when the fact that Gene's face is hidden by his hand protects his undercover identity when the picture makes the front page of the local paper.
 * Variant on MythBusters—after a day's worth of full-scale testing wrapped up as a day's worth of failed full-scale testing, Adam walked up to the cameraman and put his hat over the lens.

Real Life

 * Truth in Television: Appears a lot on news broadcasts. Chinese officials do it a lot.
 * Church of Happyology is also known for this. They go beyond just using hand on a camera, but also physically attack the camera man, then send a policeman to accuse the cameraman for unlawfully recording a conversation.
 * Michael Jackson did this frequently.

Video Games

 * Kanji does this in the opening movie of Persona 4, after beating the shit out of two goons. That's just who he is.
 * In The Sims 2, when a romantic couple are in a photobooth together and have their picture taken, the last picture in the sequence is of one of them holding their hand in front of the camera.

Web Original

 * Dana pushes the camera away, telling Zack to stop wasting film, in Episode 1 of Echo Chamber.

Western Animation

 * Total Drama Island: When a cameraman sneaks up behind Gwen to see what she's drawing (A picture of Trent without his shirt) she annoyedly covers the camera lens with her hand, and later in the TDA special Noah does the 'Talk-to-the-hand' variation of this to Sierra when she tries to interview him on the Red Carpet, though this was most probably because he was on a call with someone at the time.