window.onload = function (e) {  
    var evt = e || window.event,// define event (cross browser)  
        imgs,                   // images collection  
        i;                      // used in local loop  
    // if preventDefault exists, then define onmousedown event handlers  
    if (evt.preventDefault) {  
        // collect all images on the page  
        imgs = document.getElementsByTagName('img');  
        // loop through fetched images  
        for (i = 0; i < imgs.length; i++) {  
            // and define onmousedown event handler  
            imgs[i].onmousedown = disableDragging;  
        }  
    }  
};  
  
// disable image dragging  
function disableDragging(e) {  
    e.preventDefault();  
}