The data URI scheme is a uniform resource identifier scheme that provides a way to include data in-line in Web pages as if they were external resources. It is a form of file literal or here document.

What is inline image?

(World-Wide Web) An image that appears within the body of a web page. Most graphical web browsers can display both GIF and JPG images inline. The web browser may give the user an option to turn off inline images, to speed up the display of web pages.

How do I view an inline image?

Use F10 or alt+v to make a menu appear and in that menu go to View|Toolbars and tick the checkboxes. Now you have a menu with a View option, you can use it to display attachments inline, and also to view messages in "original html".