add image to post/db

/*
*  In WordPress Multisite, when an image is added to a blog post in edit mode, I need to add it to the DB as a post.
*  For some reason, it adds the post as an attachment to wp_1_posts instead of the correct blog's table.
*/

/*
*   all of these variables are set, and correct
*/

$imgurl     = $_POST['imgurl'];
$imgh       = $_POST['imgh'];
$imgw       = $_POST['imgw'];
$blog_id    = $_POST['blog_id'];   //    on my test box, this value is 37
$post_id    = $_POST['post_id'];


//  Switching to the blog that I want to add the image to

//switch_to_blog($blog_id);  //  <---  Verified blog_id is 37

//$wpdb->set_blog_id(37);      //  <----  This actually switches to blod id 37


// Array of data about the image. These are the four required keys

$attachment = array(
    'post_mime_type'    => 'image/jpeg',
    'post_title'        => 'image title',
    'post_content'      => '',
    'post_status'       => 'attachment'
);

//  Insert the attachment into the DB. Returns the post_id of the post

$attach_id = wp_insert_attachment($attachment, '', $_POST['post_id'] );

if ($attach_id == 0)
{
    //  TODO: ADD ERROR HANDLING
}

// Build the HTML that will go into the draft post

$ret_url = '<a href="' . $imgurl . '"><img class="alignnone size-medium wp-image-' . $attach_id . '" src="' . $imgurl .'" alt="" width="' . $imgw . '" height="' . $imgh . '" /></a>';

// Return the HTML & die
echo $ret_url;

restore_current_blog();

die();