How to export the contact photo in Mountain Lion?
Trying on OS X Yosemite 10.10.1:

On OS X 10.8 it was possible to extract a photo from contacts on the Mac user interface.
That did not work for me on the current version.
Thus I went to look in the ~/Library.

I found the picture I had taken under


~/Library/Application\ Support/AddressBook/Sources/(some long hex string)/Images/


Thus on Finder click the "Go To" menu, holding the ⌥ ALT. Click on "Library", then navigate to the Images folder.

(On my iPhone, in Contacts, I had taken a photo of a friend yesterday.
Today I wanted to file the photo, found it as above on my Mac, though with a size of 87 KB only.)