Image copyright Twitter Image caption This image is being widely shared on social media at the moment - but it dates back years

The hashtag #RealMenDontBuyGirls has been tweeted thousands of times in the past few days in connection with the abducted girls in Nigeria. It's reported that Hollywood celebrities have endorsed the campaign, but things are not exactly as they first appear.

#RealMenDontBuyGirls is trending in the US, Nigeria, Spain, the UK and elsewhere, and the vast majority of tweets call for the release of the more than 200 girls kidnapped by Boko Haram militants in Nigeria. It's being used widely together with #BringBackOurGirls, which has now been tweeted more than 1.6 million times globally.

Just as with #BringBackOurGirls, many of the tweets include images of celebrities holding signs - in this case saying, "Real Men Don't Buy Girls". Images of Sean Penn, Justin Timberlake, Ashton Kutcher, Jamie Foxx and others are being widely shared right now. But - and it's quite a big but - many of these celebrity images date back as far as three years ago. The Real Men Don't Buy campaign was started in 2011 by Ashton Kutcher and Demi Moore to fight trafficking - particularly of children - into the sex trade. It featured a series of YouTube videos with celebrities.

So how did it get linked with the case of the abducted girls in Nigeria? The first use of the hashtag on Twitter in this context was on 2 May 2014, by a woman who appears to be based in New Jersey in the US. After news emerged that Boko Haram militants were threatening to sell the girls, the hashtag took off. And as far as we can establish, the old images from the previous campaign were widely re-posted and shared - not by the celebrities or the campaign itself, but by regular Twitter users in Nigeria, the US and elsewhere. These tweets were in turn picked up by influential tweeters, and then by mainstream media. Images posted on social media are, of course, often taken out of their original context. This is a helpful guide to verification of images.

The re-adoption of the #RealMenDontBuyGirls campaign highlights just how strong global sentiment now is concerning events in Nigeria. An online "social media march" is taking place on Thursday, with people urged to spend 200 minutes on social media to support of the missing girls in Nigeria.

Reporting by Cordelia Hebblethwaite

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