image-dired-gallery-thumb-image-root-url

image-dired-gallery-thumb-image-root-url is a variable defined in `image-dired.el'.
Its value is

"http://your.own.server/image-diredthumbs"

Documentation:
URL where the thumbnail images are to be found.
Note that this path has to be configured in your web server. Image-Dired
expects to find pictures in this directory.

You can customize this variable.