I like the 2008 winner most [1], especially because it is so simple and can happen to anyone but also very easy to overlook. And most other entries could have been prevented in other languages, this one isn't.
Also, the author could claim they inspected/analyzed the visual output and the redaction appeared flawless.
At least, I assume most image viewers won't display a dialog:
Warning: suspiciously redundant image data detected. If any part of this image is supposed to be redacted, please contact your system administrator immediately.