When looking at a picture of the sun, how could you tell whether or not it's rising or setting?
Although there's no way to tell with certainty, there are a couple of clues you can look for. Let's think about what happens to the atmosphere during the day. It warms up, which means it can hold more moisture, and traffic and other activities churn a certain amount of dust and pollutants into it.
All this extra stuff in the air can make the sunset much redder than sunrise. It can also make the light more diffuse. Artists sometimes remark that the light at sunset is softer and warmer than the sharp light at sunrise.
However, rain or other weather can disrupt this pattern. Another clue is the ground, which cools down overnight. This can cause dew to condense out of the air, and mist to form in the air near the ground. If there's any rising mist or dew in your photo, chances are it's sunrise.
