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