<div class="thumb thumb-rounded thumb-slide">
      <img src="<?php echo $result['staff_signature'];?>" alt="Signature IS BLANK">

      <div class="caption">
        <input type="file" class="file-input" data-show-caption="false" data- show-upload="false" accept="image/*" id="signature" name="signature">
      </div>
    </div>
    <input type="hidden" name="imgsrc" id="imgsrc" value="<?php echo $result['staff_signature'];?>">

if($_FILES[signature]['name']!="")
    {
//file upload code
    }
else
{
$imgsrc=//get the imgsrc value using GET/POST ..whatever u are using the form

}