The box on the photographer's form

An original explanation of an invented photography project.

Our form asked photographers to record where and when each picture was taken. A final box was labelled Context. Several people left it empty because the location and date seemed to explain everything. One photograph showed a long queue outside a closed door. The photographer added that the queue had been arranged for a performance and the people were volunteers.

Without that information, a viewer might have taken the picture as evidence of a delay or a shortage. The extra detail did not alter the image, but it changed the circumstances in which we understood it. We moved the Context box higher on the form so that it was less easily overlooked.

In this passage, what does “context” mean?