One day one pic is the name of our user-contributed banner rotation program. It was called after that because, first, it was planned to rotate the banners daily.

How to submit a banner?
Upload a picture as you usually do and categorize it as "1day1pic".

What size?
1000x150

What quality do you expect?
Pictures with a good resolution, no artifact. Just use your common sense. No tag or watermark (credits are given here).

What about NSFW pictures?
Those are not allowed. Try to stay as safe for work as possible.