Mark/flag latest posts with icon

I was unsuccesfully searching for hours for a plugin or a hack, that enables my blog to flag/mark the latest posts with a “new” icon next to the post title depending on two criterias:
– the user/visitor has already read (icon shows up) the post or not (icons shows not up)
– the post should be flagged/marked with the “new” icon from wp or a plugin for a maximum predefinable time since the post has been published, disregarding whether the user/visitor has read the post.

What I am looking for is what these guys have at their blog: http://www.docmorris-blog.de

Their solution seem to use the 2 criterias:

– If I already read the post – the “new” icon disappears automatically next time I visit the blog (detected through a browser cookie … I checked that)
– If I visit the blog and have NOT already read the post, but the post has been published i.e. at the day before – the “new” icon disappears automatically, too.

Any hints or an ideas whether there is a plugin or hack to do it the same way like docmorris-blog.de ?

Thanx in advance!