Sample email validation by showing images

<script language="JavaScript" type="text/javascript">  
function emailCheck(email){  
 var reg =/^[a-z_0-9]+@+[a-z_0-9]+(.com|.edu|.net|.mil|.co.uk)$/  
  if (reg.test(email)) {   
   document.getElementById("check").innerHTML = "<img src='images/check.gif'>"  
  }else{  
   document.getElementById("check").innerHTML = "<img src='images/uncheck.gif'>"  
  }  
}  
</script>  
<input type="text" id="email" onkeyup="emailCheck(this.value)">   
<span id="check">  
 <script>   
  emailCheck()  
 </script>  
</span>