I believe that Marvin Minsky is the origin of the story. He tells it in the second half of the 3 minute video Embarrassing mistakes in perceptron research. This version of the story is not so simple as sunny/cloudy, but that the two rolls of film were developed differently, leaving to a uniform change in brightness.

The first half of the video is a similar story about distinguishing musical scores using the last note in the lower right corner. Somewhere,* quite recently, I heard people argue that this story was more credible because Minsky makes a definite claim of direct involvement and maybe the details are a little more concrete.

[How did I find this? The key was knowing the attribution to Minsky. It comes up immediately searching for "Minsky pictures of tanks." But "Minsky tank neural net" is a poor search because of the contributions of David Tank. Note that the title of the video contains the word "perceptron," suggesting that the story is from the 60s.]

* Now that I read Gwern's comment, it must have been his discussion on Reddit a month ago.

Added, a week later: I'm nervous that Minsky really is the origin. When I first wrote this, I thought I had seen him tell the story in two places.