It can. Most of the time, they don't have any meaning.
I've seen portraits of people in dignified setting. But basically it is a picture of the person - taken nicely;
Other times, I've seen pictures that tells the story behind the portrait:
http://www.acjournal.org/holdings/vol10/s_special/images/bowers/image001.jpg
http://images.artnet.com/artwork_images/911/113813.jpg
So it all depends...
Good Luck...