For humans, eyesight is the primary sense. We use it for communication, navigation, learning, pleasure, everything. We don't have strong sense of smell like dogs and cats, we don't feeling whiskers, and even our hearing, which is vital and quite versatile, is less sensitive then that of many animals, and degrades as we age. Eyesight is everything for humans. Blind people get by, of course, but with difficulty.
Manipulate what people see, and you've got the keys to the kingdom. Public opinion can be easily swayed by controlling what is seen and what is hidden on television, in movies, newspaper photos, internet, the list goes on. As the old saw goes: a picture is worth a thousand words.
How fast do you think it would take the public to put an end to the war in Iraq if, after every accidental or negligent homocide of a woman or a child by friendly fire, photos of torn and mangled bodies were shown in western media? These photos do exist, but they are not shown, and for a reason. Those in charge remember how photos of the consequences of their decisions undermined support for the Vietnam war. Recall the photo of the naked little girl running from her village with napalm burns on her skin. Or the film of the South Vietnam officer summarily executing a suspected NVA spy on a city street by simply walking up to him and firing a revolver into his head, and the blood shooting forth from the wound as the handcuffed man fell dead. Such images don't show the whole story, but serve to shock you into seeing one powerful part of the story and play a large part in forming your opinion.
A more blatant and clumsy example is the famous video of George Bush standing on the flight deck of an aircraft carrier after invaing Iraq: in the background on the superstructure of the ship was a giant banner that read "Mission Accomplished". Later, if you viewed that video on official White House website, the video was letterboxed such that the banner was cropped out.
This isn't new, either. The communists were very good at this, recall the famous removal of Trostky from a photo of Stalin giving a speech.
If you remember the Arnold Schwarzenegar movie Running Man, you can recall the scene in which the main character is framed for murder by editing the cockpit video to make it appear as if he had opened fire on protesters, when he had in fact done the opposite. At the time that movie was released, we all had a laugh at the science fiction of that scene, but the technology to do that has advanced rapidly.