Face headers are essentially a funkier version of X-Face
ones. They describe a 48x48 pixel colored image that’s supposed to
represent the author of the message.
The contents of a Face header must be a base64 encoded PNG image.
See https://quimby.gnus.org/circus/face/ for the precise
specifications.
The gnus-face-properties-alist variable affects the appearance of
displayed Face images. See X-Face.
Viewing a Face header requires an Emacs that is able to display
PNG images.
Gnus provides a few convenience functions and variables to allow easier insertion of Face headers in outgoing messages.
gnus-convert-png-to-face takes a 48x48 PNG image, no longer than
726 bytes long, and converts it to a face.
gnus-face-from-file takes a JPEG file as the parameter, and then
converts the file to Face format by using the
gnus-convert-image-to-face-command shell command.
Here’s how you would typically use this function. Put something like the following in your ~/.gnus.el file:
(setq message-required-news-headers
(nconc message-required-news-headers
(list '(Face . (lambda ()
(gnus-face-from-file "~/face.jpg"))))))