In fact, this dystopia may never come about. There are great technical difficulties in producing and transmitting high-quality moving computer images, which have not yet been overcome; and even if they are, there is a serious doubt as to the likely profitability in producing such material. If it does not promise to make someone a fortune, the chances are that it will never see the light of day.
We should worry, anyway. The information revolution is throwing up problems for us right now, but they do not concern pictures so much as words.
The simple transmission of words through electronic mail raises potentially immense issues of principle concerning censorship and control. The technology is spreading at a rate difficult to believe. The worldwide voluntary network Internet, which connects computers seamlessly through telephone lines, is thought to be growing at 10 per cent a month. Perhaps 20 million people are connected already - no single body controls it, so no one really knows. Many other mail systems exist that are not connected to the Internet; but all will be eventually, so any computer in the world will be able to reach any other, just as any telephone can.
The computer-messaging systems connected to the Internet already cover nearly every country in the world. On them are discussed every subject in the world; and every viewpoint is represented. Whatever you believe should be censored is being published.
It need not be pornography, though from my desktop I can access discussion groups on sado-masochism, bestiality and paedophilia. I can also find people to tell me that the Holocaust was a Jewish myth, and that the Armenians committed genocide on the Turks in 1914-18. And detailed instructions on making explosives are available.
Whatever information you believe should be kept from children can be acquired by a determined youngster with a computer and a modem. And it's cheap: once connected, it costs nothing extra to access anywhere in the world. At present, the child has to be unusually determined and intelligent to get the software to work properly, but this is changing rapidly.
Although there has yet to be a test case in the courts, much of this stuff may be illegal to receive in this country. But it is difficult to see how such laws can be enforced, if the source of the messages is outside this country. It has proved difficult enough to control satellite broadcasters, and they are large commercial operations, vulnerable to all kinds of pressure. The broadcasting of computer messages needs no special equipment, and senders can be difficult to identify, let alone suppress. Anyway, the really dangerous ones are not in it for financial gain.
Faced with these problems, governments have two directions in which to go: either they can abandon censorship, or they must try to control every word. The former approach has been adopted in America. Taking the First Amendment seriously, they have allowed anything to be sent down the Net. Some pictures which offend local standards have been censored in places where there are local standards to be offended. But speech is absolutely free. If you want to advertise for soul-mates to share an interest in sodomising St Bernard dogs, go ahead.
In theory, things are quite different in Britain. The University of Kent, which is the main supplier of Internet mail here, will not carry some of the more controversial discussion groups. But that does not and cannot prevent anyone from connecting to a computer in America, thereby bypassing the university's regulation. Whatever is permitted anywhere on the net becomes available everywhere.
In effect, Internet has exported the First Amendment throughout the world. Well, almost throughout the world: in China, they have heard of free speech and have opted for a policy of absolute censorship.
Totalitarian societies have a dishonourable history of trying to control media technologies. In the Thirties, Hitler and Stalin passed laws against the possession of shortwave radios to prevent ideological pollution from abroad. Under Brezhnev, unauthorised use of a photocopier was a criminal offence, to prevent citizens from corrupting each other. Computer networks have already been used to subvert totalitarian ambitions: during the 1992 coup against Gorbachev, the university network in the Soviet Union was used to distribute detailed and accurate news reports from independent news agencies.
The Chinese government has good reason to want to ban them. But it knows it can't. Such networks are essential to the sort of modern economy the Chinese are desperate to build. A national law published in February provides for the control of all computer networks by the security police.
Article 6 states: 'The Ministry of Public Security shall be in charge of safeguarding computer information systems. The Ministry of State Security, the State Secrecy Bureau and relevant State Council departments shall carry out work pertaining to safeguarding computer information systems within the lines of authority prescribed by the State Council.'
And Article 7 continues with a catch-all clause: 'No organisation or individual may use computer information systems to engage in activities that endanger national or collective interests.'
This will need an army of electronic censors to enforce, reading electronically over everybody's shoulder. But, technically, that will not be difficult.
If any law can quash the use of computers to promote freedom of thought and expression, this is it. But the question is whether any law can. Looking at these two prospects for the future, I do not know whether complete censorship or complete freedom frightens me most.
The writer edits the Computer page of the 'Independent'.