I need help for the "New to you" code.

The whole story:

I am making a Forum for my website.
I would like to have a picture on the forum on each post that a user hasn't seen.
The picture disapears when that user has seen the post.

I tried the "New to you" code, but it only does the "new to you"on that page.

I would Like the picture to go only after the user has seen that post, not only the list of posts.

In other words, I want to have a New t you feature that show the picture on an other page than the page of the post itself.

Hum.... I'm not shure if that is clear...

Well I hope you understand and can help me.