how to org mode image absolute path of export html?

The way to do this is to register a new kind of link in org-mode, using org-add-link-type. That lets you supply a custom export format.

org-add-link-type requires a prefix, a "what happens when you click the link?" function, and an export function.

I use a prefix of img, so my links look like [[img:logo.png][Logo]]. My image files are in ../images/ (relative to the .org files), and from the webserver they show up in /images/. So for those settings, putting this in .emacs provides the solution:

(defun org-custom-link-img-follow (path)
  (org-open-file-with-emacs
   (format "../images/%s" path)))

(defun org-custom-link-img-export (path desc format)
  (cond
   ((eq format 'html)
    (format "<img src=\"/images/%s\" alt=\"%s\"/>" path desc))))

(org-add-link-type "img" 'org-custom-link-img-follow 'org-custom-link-img-export)

You'll probably need to amend the paths for your setup, but that's the recipe. As you'd expect, C-hforg-add-link-type will give you the full gory details.

Oh, and for what it's worth, here's the code I'm using for inter-post links (like [[post:otherfile.org][Other File]]). There's a little Jekyll magic in the output format, so watch the double-%s.

(defun org-custom-link-post-follow (path)
  (org-open-file-with-emacs path))

(defun org-custom-link-post-export (path desc format)
  (cond
   ((eq format 'html)
    (format "<a href=\"{%% post_url %s %%}\">%s</a>" path desc))))

(org-add-link-type "post" 'org-custom-link-post-follow 'org-custom-link-post-export)