CODE EXAMPLE FOR JAVASCRIPT

on function change body background image

function replace() {
  document.body.style.backgroundImage = 'url(https://lh6.ggpht.com/8mgTDZXaLMS1JsnF28Tjh6dahHwN1FqcXCVnifkfppmNLqnD-mPBuf9C1sEWhlEbA4s=w300)';  
}