Around the world, explicit images of children and teens are circulating on the web.   Sometimes they're willingly shared with a girlfriend or boyfriend, other times kids are tricked into sharing nude photos by a perpetrator.   Now there's a new tool to help young people get some of them removed.  KMOX's Megan Lynch and author Julie Smith talk with National Center for Missing and Exploited Children spokesman Gavin Portnoy about Take It Down.