var clickmessage="Right click disabled on images!"

function disableclick(e) {

  if (document.all) {
    if (event.button==2||event.button==3) {
      if (event.srcElement.tagName=="IMG"){
          alert(clickmessage);
          return false;
      }
    }
  }
  else if (document.layers) {
    if (e.which == 3) {
      alert(clickmessage);
      return false;
    }
  }
  else if (document.getElementById){
    if (e.which==3&&e.target.tagName=="IMG"){
      alert(clickmessage)
      return false
    }
  }
}

function associateimages(){
  for(i=0;i<document.images.length;i++)
  document.images[i].onmousedown=disableclick;
}
/*
if( document.all )
  document.onmousedown=disableclick
  
else if( document.getElementById )
  document.onmouseup=disableclick

else if( document.layers )
  associateimages()
  */