If there were people in the photo conducting a celebration, that would let you know that it was the solstice, because people aren’t allowed near the stones at other times.
I doubt, though, that that is common knowledge to anyone from outside of the UK, so whoever designed that test has an unconscious bias.
Exactly, and this is assuming that that detail was even in the photograph; I am only guessing - OP didn’t say so.
I don’t even know how widely it would be known to Brits, although Stonehenge has been in the news recently, on account of people throwing paint on it and bothering the lichen, so it might have been mentioned in those news reports.
I wrongly said that the Stonehenge photo was a test - OP said it was a training course.