session variable in select query showing picture from database

I'm trying to show picture from database. Everything works until I add
variable into where part of the query.

It works with plain number. example ...WHERE id=11... ...picture is shown on
the page.

Here's the code that retrieves the picture. show_pic.php

<?php
function db_connect($host='********', $user='********',
$password='********', $db='********')
{
mysql_connect($host, $user, $password) or die('I cannot connect to db: ' .
mysql_error());
mysql_select_db($db);
}
db_connect();
$band_id = $_SESSION['session_var'];
$query="SELECT * FROM pic_upload WHERE band_id=$band_id";
$result=mysql_query($query);
while($row = mysql_fetch_array($result))
{
$bytes = $row['pic_content'];
}
header("Content-type: image/jpeg");
print $bytes;


exit ();
mysql_close();
?>


other page that shows the picture

<?php
echo "<img width='400px' src='./show_pic.php' />";
?>

Any help would be appreciated...