Joshua, “change with time?” What kind of change would you think? A picture taken now would of course be only one “time”. It would need something from another time to compare. Let’s say a building. When was it built, what was there before it was built. A paved road, when was it paved?
The National Park was just an example of how a photograph can be evidence, Joshua. Do you have an imagination? How might someone use image comparison in problem solving?
You want to teach critical thinking or critical reasoning, what will your students do with what you teach them? Teach critical thinking or solve problems?