The value of 'content' for the media is rarely constant, but it's a useful to work from the principal that if an editor wants something, be it words or pictures, sound recordings or video, then it's worth something.

Most people taking most pictures most of the time do not consider them to have more than sentimental value.

But circumstances can and do change.

A snapshot of a teenager on a beach in Thailand taken to show family and friends was worth little, if anything, until she was killed a few hours later. Then, every picture of her taken on that holiday became valuable.

According to Journalism.co.uk, Newsvine - a site which lets "readers tag, comment or chat" on Associated Press wire stories, "publish links and write their own columns" - hands over 90 percent of the revenue from adverts on their work.

Knowing just how many hits it takes to earn a few cents from Google ads, that hardly seems a good deal.

Media organisations can, and do, make money trading material, be it selling video or still photographs or syndicating their writings of their star columnists.

While journalists, especially freelance journalists, who depend on their writing and reporting, still photographs, video footage or radio reports for their incomes, may feel that their livelihoods are threatened by editors choosing apparently free contributions, there is another, more basic question of fairness.

According to Bill Hagerty, editor of British Journalism Review, speaking at a roundtable event hosted by The Guardian in January 2006, "it is wrong to solicit and not pay".

Simon Waldman from Guardian Unlimited, The Guardian's online operation, said that a move by the Telegraph group to encourage contributions without paying for them and simultaneously expecting contributors to accept all liabilities was "tightfisted and inept".

Witness contributors with images they think may have a commercial value are probably best advised to negotiate payment. If the picture is good, then an editor will probably pay.