how about comment on image page ?

The image page is using something like "image content type"; which has its own setting for enabling comments. See Administer -> Structure -> Content Types. There you can enable/disable comments for any of your content types by editing each content type separately.

Hi,

Just updated to the dev version and still not seeing any "image content type" under admin/structure/types. The only related content type I have is Gallery.

Am I missing something?

A gallery is of type node and therefore you can enable comments under admin/structure/types.
The image is a media of type entity (?), and seems to be not supported by the comments module (admin path is admin/config/media/file-types).

Further information:
#993590: enable comments on individual media entities
#731724: Convert comment settings into a field to make them work with CMI and non-node entities

I have not testet it, but the only module i found which might can handle "comments" is reply. There is just a dev-module.

Marking as duplicate of #951752: Allow commenting on media items..