php

<form .....>
<input style="width:350px" name="profpicURL" id="profpicURL" title="URL for an image" alt="URL for an image" onkeyup="document.getElementsByName('profPic')[0].src=this.value" type="text">
...
$backPicture = $_POST['profPicURL'];
<input type="hidden" id="profpic" name="profpic" value="<? echo $backPicture; ?>" />
...
</form>