OK, I looked on Apple's support site also and am still unable to add a picture to a contact in Address Book.
The site said to double-click the picture field, click "Choose" and locate the picture to use. Problem - when I double-click, there is no "Choose". It just toggles the Blue perimeter on and off.
I tried the easiest way - drag the picture and drop it in the picture box. I get the Green Plus button, but the picture does not get added - the square is still blank.
I am feeling quite stupid now. Any ideas are welcome; and you may ridicule me too if you wish