laravel 5.4 embed image in mail

I have just upgraded my 5.2 install of laravel to 5.3 and then to 5.4 following the official upgrading methods.

I am now trying to use one of the new features, to create a markdown formated email.

According to the documentation found at: http://ift.tt/2lQHtGR

To embed an inline image, use the embed method on the $message variable within your email template. Laravel automatically makes the $message variable available to all of your email templates, so you don't need to worry about passing it in manually:

However, this:

<img src="">

will produce the following error:

Undefined variable: message

Am I missing something? Or is there something undocumented in the upgrading guides?

via Chebli Mohamed