in glip you can comment on images by click an area for commenting for say if you are sharing a design for a website. the full page is hsared in one jpen. you can click on the navigation of the or area of the site. its more collaborative and easier since the pins are attached to specific points.
@Adric, there is an add-on that allows you to edit/post images. It is not exactly what you are asking for but can be used to put text/comments in images.
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