Currently, 4chan has 3 tab icons for thread reply statuses. A plain clover for no new replies, a white exclamation point for new replies and a red exclamation point for a reply to one of your posts.

I think there should be 3 more tab icons added.

For threads with a new image reply: Two white exclamation points
For threads with a new image reply and a reply to one of your posts: One white and one red exclamation points.
For threads with a new image that is also a reply to one of your posts: Two red exclamation points.