list monthly post, but hiding author for current and previous month

I try to set up a contest category for a photo-site.

The idea is that we have a monthly photo contest, and we want the photo posts to be “anonymous” (as in not showing the photographer/author in the entry-meta) for the current and previous months.

For entries older than one month will reveal the names/usernames of the photographers (=author).

So I need two things: To list post by months (current and previous with hidden authors), and when you view a post in the current and previous contest months the authors are also hidden.

Thanks in advance for your help,
Paul