Getty Images, the world's largest photo agency, has made vast swathes of its library free to use, in an effort to combat piracy.

Millions of images - including famous shots of Marilyn Monroe and Barack Obama - will now be available without cost to blogs and social media sites.

The photos will be "framed" with a code that links back to Getty's website.

Getty said it had made the move after realising thousands of its images were being used without attribution.

"Our content was everywhere already," said Craig Peters, a business development executive at the Seattle-based company.

"If you want to get a Getty image today, you can find it without a watermark very simply," he added.

"The way you do that is you go to one of our customer sites and you right-click. Or you go to Google Image search or Bing Image Search and you get it there. And that's what's happening."
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