Whether it is a picture - for example, a simulation of the new marketing plan needs to be fed, or a PDF file, a speech, or you can preview any file in Confluence. You can place a hot spot anywhere in the preview of the dialogue after the start and then add your comment.
I wish to file a comment:
- Click the file preview thumbnail or chain.
- Drag a hot spot from the bottom of the preview file (Pin) icon placed anywhere you want to comment.
- After you add a comment to save (the Save) .
Reviews and comments page hot spot is the same ( inline Comments ). You can use @mentions and links , and then placed the number of hotspots icon. You can even add simple macro Macros , for example using Wiki markup automatically add the macro code. Any user with a page to add comments can operate on file comments.
When you preview the file, you can see the comments in this hot version of the file that already exists. Select a hot spot to view comments.
Once the dialogue for the completion of the review, you can turn off the comments to see the hidden (or any response). If you need to review again be resolved, you can choose to play them again. In view into the View 
> solve Reviews (Comments to Resolved) .
- Resolve comments (Resolved comments): More options (more options) button to show or hide comments have been resolved.
- Reviews (Comments): drag a file into the hot spot to comment.
If your files are stored on a Web server and is adding a URL to Confluence or your file can not be previewed (such as video, compressed files and other file types), you can not add a comment to this file, you can not add to a file.
When you upload a new version of a file, your comment will be what happens?
Comments only for a specific file version. This is mainly to avoid the file or picture hot spot has been repeatedly modified two resulting confusion.
To view a previous version of the file list Reviews:
- Click on a thumbnail or link to a file into the preview.
- In the top left drop-down to select the file name and select the previous version.
- For comments all hotspots of the previous version will be displayed.
How much you can add comments in a file?
In fact, the file number of comments for Confluence is no limit. But Confluence only display 100 reviews. Please refer to CONFSERVER-43397 - Prevent the Users from Adding More pinned Comments Within last 100 IT and the Document GATHERING INTEREST for more information.
https://www.cwiki.us/display/CONF6ZH/Share+and+Comment+on+Files