When exporting an org file containing latex fragments with option

#+OPTIONS: tex:dvipng

in the html file the png image src attribute's value is not a valid URI. 
<img src="e:/dir/sth.png" ...>  while it should be <img 
src="file:///e:/dir/sth.png" ...>  for the browser to work. In my config 
I have  (setq org-preview-latex-image-directory "E:/tmp/ltximg/") so 
that all images are created in a single directory and don't clutter my 
org file directory.

I fixed this issue for me by modifying `org-html--format-image' function 
of ox-html.el file as follow:

(defun org-html--format-image (source attributes info)
   "Return \"img\" tag with given SOURCE and ATTRIBUTES.
SOURCE is a string specifying the location of the image.
ATTRIBUTES is a plist, as returned by
`org-export-read-attribute'.  INFO is a plist used as
a communication channel."
   (if (string= "svg" (file-name-extension source))
       (org-html--svg-image source attributes info)
     (org-html-close-tag
      "img"
      (org-html--make-attribute-string
       (org-combine-plists
        (list :src (concat "file:///" source)
	     :alt (if (string-match-p "^ltxpng/" source)
		      (org-html-encode-plain-text
		       (org-find-text-property-in-string 'org-latex-src source))
		    (file-name-nondirectory source)))
        attributes))
      info)))

I just changed (list :src source ...) to (list :src (concat "file:///" 
source).

I don't know if it is an acceptable way or it further causes bugs in 
other places.
Hope that this will find the proper way and fix it.

(emacs-version) = "GNU Emacs 26.3 (build 1, x86_64-w64-mingw32) of 2019-11-01"
(org-version) = "9.3.6"

Emacs Admirer,
Bibek Panthi