I'm working on ePen, an editor for novels which can create an HTML export. To make it easier for readers to follow the story, I thought about supporting bookmarks which are visible on the page (so you can mark part of the text or drag an image somewhere where it sticks). The information should be saved in a cookie and reloaded when the reader returns so they can quickly jump to the page and place where they left off.
What are my options? Does something like that already exists? Have you seen something similar already?