U.S. Border Patrol agent Richard Funke looks for footprints from illegal immigrants crossing the U.S.- Mexico border near Nogales, Ariz., in 2010. John Moore/Getty Images hide caption

itoggle caption John Moore/Getty Images

Brazilian slave laborers stop their work to listen to a Labor Ministry inspector explain their legal rights, on the Bom Jesus farm in the Amazon basin in 2003. Rickey Rogers/Reuters /Landov hide caption

itoggle caption Rickey Rogers/Reuters /Landov