This works for me
<input name="picture" type="file" onchange="alert(this.value)" class="file" size=20/>
for use upload button as image try this
<style>
div.fileinputs {position:relative; display:inline;}
div.fakefile {position:absolute; top:0px; left:0px; z-index:1;}
input.file {position:relative; text-align:right; -moz-opacity:0; filter:alpha(opacity: 0); opacity: 0; z-index:2;}
<style>
<div class="fileinputs">
<input name="picture" type="file" onchange="alert(this.value)" class="file" size=1/>
<div class="fakefile">
<img src="images/browse.gif" align="middle" alt="browse" title="browse"/>
</div>
</div>
so the input field is hidden, and when u click image - the selection dialog appears, but emulate this dialog from js imposible, yep.
But you can also write the plugin/hack for browser)