JavaScript - ocultar y mostrar imagenes textos y formularios

<script type="text/javascript">

function verform()

{

document.getElementById("frm").style.visibility="visible";

document.getElementById("img").style.visibility="hidden";

}

</script>

<form id="frm" style="visibility='hidden'">

Campo 1: <input type="text" name="firstname" size="20"><br>

Campo 2: <input type="text" name="lastname" size="20"><br>

</form>

<input type="button" onclick="verform()" value="Mostrar">

<input type="image" onclick="verform()" src="imagen.gif" id="img">