I wasn't paying enough attention -- Ada Island is at the extreme south end of the Montenegrin coast, so the proper caption should be Yugoslav - Albanian border.

There's some mention of the border near the end of this article:

http://www.netnude.com/main/info/greece/croat001.html

Can anybody help to locate this island? http://store.corbis.com/search/about_pic.asp?navid=decorate/prints&imageid=10783847&alphaimageid= Jesper