disable right click on img tag code example

Example: html picture disable right click

<script type="text/javascript">
    var message="Function Disabled!";

    function clickIE4(){
        if (event.button==2){
            alert(message);
            return false;
        }
    }

    function clickNS4(e){
        if (document.layers||document.getElementById&&!document.all){
            if (e.which==2||e.which==3){
                alert(message);
                return false;
            }
        }
    }

    if (document.layers){
        document.captureEvents(Event.MOUSEDOWN);
        document.onmousedown=clickNS4;
    }
    else if (document.all&&!document.getElementById){
        document.onmousedown=clickIE4;
    }

    document.oncontextmenu=new Function("alert(message);return false")
</script>