You should just have to update to reference the blog post content on this page like:
WA_getCMSContent($database_PowerCMSConnection, $PowerCMSConnection, 'BlogPosts', 'Content', false, $row_BlogRS['ContentPageSetOrder'] )
so the code would be:
<?php
$blogContent = WA_getCMSContent($database_PowerCMSConnection, $PowerCMSConnection, 'BlogPosts', 'Content', false, $row_BlogRS['ContentPageSetOrder'] );
$blogImage = preg_match('/<img [^\r\n]* src="([^"]*)/i',$blogContent,$retVal);
?>