Вставляете в head:

<script language="JavaScript1.2"> 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() </script>

Пример