It looks like email-clients are blocking encoded images in the email. I got a scenario where i can properly view the HTML-source (including the encoded image) of the email when copying this to a webpage, like test.html. The encoded image is displayed in the browser However, when receiving the email containing the encoded image, the image is blocked, despite the fact that the source of this email is the same as before sending. A few number of email-clients have been tried (outlook, hotmail, gmail), the they all work the same. Is there a way the make the email 'trusted' before sending? Or is there another way to make sending encoded images in an email work?
The suppport for embedding images in mail and displaying the images seems to be limited see this post.
Embedding images can be done without using data URI's but with embedding as attachment see here for an example and explanation.