<input type="file" name="image" id="file">
<input type="submit" value="Upload / Edit picture" name="upload_picture" id="upload_picture" class="btn" />
<script>
$(function(){
$("#upload_picture").hide();
$("#file").change(function(){
if ($("#file").val() != ""){
$("#upload_picture").show();
}
else{
$("#upload_picture").hide();
}
});
});
</script>