astrophotography - How accurately can you tell the time using a photo of the stars?

To make a clock you need something that changes predictably with time, and stars are nearly constant, making them poor clocks.

The stars do move across the sky each night, but since the morning stars of winter become the evening stars of spring, and the sky looks different in different locations you need to know the date of the image, the location of the photo, and the exact direction of the photo. That could give sub 10 min accuracy. Unfortunately while date and location may often be recorded with a photo, exact direction is not, unless the horizon is visible in the image.

Without that information, and it is possible to 'get lucky'. For example, if there are two or more planets in the shot, their locations could be measured to give at least the date of the photo. Similarly if a rare event like a nova is visible that can offer dating information. If the shot happened to catch a bright meteor, and the date was known well enough, you could get almost 1 second accuracy. Variable stars might also give the chance of at least dating the image.

With no planets you can use the very slow proper motion of the stars. With a good enough telescopic shot of the night sky you can be quite accurate, but with a wide view of a camera you wont be able to get enough accuracy to give any useful date.

The exposure time of a typical camera is to short to capture any stars. If you just point and shoot at tye sky, you just get black. To capture images of stars you would need a timed exposure. A telescope would help too.

So if you photographer wanted to create an image which could be timed accurately, and they had time to prepare for it, or it was a lucky shot this might be possible, otherwise not.