[devote]

<script type="text/javascript">
    function test( self ) {
        if ( self.value != "" ) {
           document.getElementById('file2').style.display = 'block';
        }
    }
</script>
<input id="file1" type="file" name="pic1" onchange="test( this )" />
<input id="file2" type="file" name="pic1" style="display: none;" />