How To Make Query Select Option Results

I have a Managers table in my SQL DB and it has a ManagerID, MgrName and MgrPhoto field base...

I can code a form with a select button that displays a drop down with the managers in it as choices, but am a little confused as to how I would make the PHOTO (MgrPhoto) change to the corresponding ManagerID that is selected from that option drop down since the SELECT CODE in the form only queries the ManagerID / MgrName combo for the choice.. The photo is below that drop down box and how to make it change to whatever photo is assigned to the selected ManagerID / MgrName ?

Here is the form code with query :

<form enctype="multipart/form-data" action="updatemanagerphoto.php" method="POST">
<select name="ManagerID" id="manager" style="width:400px" class="form_textbox">
<?
$db_connect= mysql_connect($db_host, $db_username, $db_password);
mysql_select_db($db_name, $db_connect) || die(mysql_error());
$sql_query= "SELECT * FROM Managers ORDER BY MgrName ASC";

[code]....