Calculate the average colour of an area in an image
imagemagick
Solution
I would crop to the area you are interested in then resize it to 1 pixel. Then get the value of that pixel.
Problem
The goal is to lay a caption on top of an image and set the text colour to one that will contrast with the background it is positioned on top of. To that end, I wish to calculate the average colour of the area inside the red rectangles in the following images: