Limited control of comments in regards to attachements.

[sterlo]

Attachments default to using the attachment page: "?attachment_id=###"

If "Allow people to post comments on new articles" was checked (as it is by default) then people can post comments on these assets.

There's no way to turn that off on any existing asset.

One solution is to disable that before uploading any assets.
Then...delete all existing assets and re-upload them...

I think it's reasonable to allow people to disable it on a per asset basis since it's something you can do on a per post/page basis.

IMO: It shouldn't be an all or nothing feature.

[sterlo]

As per nacin I tested to see if comments on the asset were disabled if the parent (if one existed) had it's comments turned off.

It did not.

[sterlo]

Duplicate of #8177 and #9839

[sterlo]

Possible solution: ​http://wordpress.org/extend/plugins/attachment-page-comment-control/