Description:
------------
Converting a database blob to a PNG image sometimes produces an image of random vertical lines. When the image is regenerated a different pattern is produced.

Reproduce code:
---------------
<?php
	// reference this file as <img src="signature.php?image_id=##">
	if ( isset($_GET['image_id']) && $_GET['image_id'] != '' ) {
		if (isset($_SESSION['user'])) mssql_connect('server',$_SESSION['user'], $_SESSION['pass']);
		$result = mssql_query("SELECT image FROM image WHERE image_id = {$_GET['image_id']}");
		if (mssql_num_rows( $result ) == 0 ) die("NO ATTACHED IMAGE");
		$row = mssql_fetch_row ($result);
		if ($row[0] == '') die("NULL IMAGE");
		$handle = imagick_blob2image( $row[0] ) or die("Invalid image BLOB");
		imagick_convert( $handle, "PNG" ) or die("Conversion to PNG Failed");
		header( "Content-type: " . imagick_getmimetype( $handle ) ) ;
		print imagick_image2blob( $handle );
	}
?>

Expected result:
----------------
The image stored in the database.

Actual result:
--------------
Random vertical lines varying with each attempt.