Minecraft wiki entry for Herobrine, associated text: MHF_Herobrine (no beard).
The original screenshot featuring Herobrine.
Another screenshot taken on the same seed from the same position.
A more recent screenshot by Copeland of the same house from his original Herobrine screenshot.
A blurred changelog for Beta 1.7 that Notch posted on twitter, with the words "Removed Herobrine" at the bottom.