mailer

// Create the message
$message = Swift_Message::newInstance('My subject');

// Set the body
$message->setBody(
'<html>' .
' <head></head>' .
' <body>' .
'  Here is an image <img src="' . // Embed the file
     $message->embed(Swift_Image::fromPath('image.png')) .
   '" alt="Image" />' .
'  Rest of message' .
' </body>' .
'</html>',
  'text/html' // Mark the content-type as HTML
);

// You can embed files from a URL if allow_url_fopen is on in php.ini
$message->setBody(
'<html>' .
' <head></head>' .
' <body>' .
'  Here is an image <img src="' .
     $message->embed(Swift_Image::fromPath('http://site.tld/logo.png')) .
   '" alt="Image" />' .
'  Rest of message' .
' </body>' .
'</html>',
  'text/html'
);