A hypothetical question

On your way out of the lab with the machine that will send a tweet back in time, you run into another old friend who is working late at the office. She is extremely excited about a new device she is about to test, and brings you into the lab to see it.

It is a camera that can take a picture of any event in the past, but with limitations. Because of the technology used, the image recorded will be something seen by a human eye. The machine can take a photo of anything a human being has seen.

They will test it tomorrow, but have not decided on a moment to record. They are also concerned that certain delicate parts of the machine will break when it is used. If that happens, it will take at least two years to repair. Your friend asks you what image you think they should try to capture.

What do you suggest?