Changer image sans frame

<script language="JavaScript">
  function changerImage(nom_nouvelle_image) {
    document.images["imgAChanger"].src=nom_nouvelle_image;   
  }    
</script>

<img name="imgAChanger" src="toto.jpg" width="142" height="61" border=0>
<br />
<input type="button" onClick="JavaScript:changerImage("titi.jpg");" value="Changer d'image">

<script language="JavaScript">
  function changerImage(avance) {
    var nombre_image_max = 10;
	var Chaine = document.images["imgAChanger"].src;
	var positionDebut = Chaine.lastIndexOf("/");
	var positionFin = Chaine.lastIndexOf(".");
	var num = Chaine.substring(positionDebut+1, positionFin);
	if(avance==1) {
		if(num<=nombre_image_max) num++;
	}
	else {
		if(num!=0) num--;
	}
	alert(num);
	document.images["imgAChanger"].src=num+".jpg";   
  }    
</script>
<p align="center">
<img name="imgAChanger" src="1.jpg" width="142" height="61" border=0 />
<br />
<input type="button" onClick="JavaScript:changerImage(0);" value="<" />
<input type="button" onClick="JavaScript:changerImage(1);" value=">" />
</p>