Mu4e HTML images are not shown by default. This gives you a way to toggle them on.

mu4e-html-images.el

    ;; mu4e toggle html images
    (defvar killdash9/mu4e~view-html-images nil
      "Whether to show images in html messages")
    
    (defun killdash9/mu4e-view-toggle-html-images ()
      "Toggle image-display of html message."
      (interactive)
      (setq-local killdash9/mu4e~view-html-images (not killdash9/mu4e~view-html-images))
      (message "Images are %s" (if killdash9/mu4e~view-html-images "on" "off"))
      (mu4e-view-refresh))

    (defun mu4e-shr2text (msg)
      "Convert html in MSG to text using the shr engine; this can be
used in `mu4e-html2text-command' in a new enough emacs. Based on
code by Titus von der Malsburg."
      (lexical-let ((view-images killdash9/mu4e~view-html-images))
        (mu4e~html2text-wrapper
         (lambda ()
	       (let ((shr-inhibit-images (not view-images)))
	         (shr-render-region (point-min) (point-max)))) msg)))
    
    (define-key mu4e-view-mode-map "i" 'killdash9/mu4e-view-toggle-html-images)

Thanks, dude.