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Human trafficking

Sexual exploitation is the bmost common driver of human trafficking, which UNODC terms "one of the world's most shameful crimes." In 2005, the International Labor Organization estimated the number of victims at any given time at 2.4 million, with annual criminal profits of about $32 billion.

Victims of human trafficking have been found in at least 137 countries. They live under constant threat; their passports are often stolen, and they may have no knowledge of the local language if they have been trafficked between countries. The rescued women in the picture live in border shelters set up by Maiti Nepal, an organization fighting the sex trade in Nepal and the trafficking of girls and women into India.

Globally, one-fifth of victims are children, who are often used for coerced begging or pornography. They may also be favored as laborers in certain sectors (because of their small hands), such as sewing luxury goods, or may be enslaved as soldiers in war zones.

Human trafficking is an escalating problem in Europe, where there are well-established markets for illegal sex and labor.

(Read more: Saudi princess charged with US human trafficking)

"The availability of young laborers and lack of employment opportunities in African, Middle Eastern and East Asian countries is likely to increase migration flows towards the EU," Europol said in a 2013 report.

Jonas Gratzer | LightRocket via Getty Images