In 1.6.7 the user interface images are no longer in the "images" directory, but
are in the "skins/common/images" directory.
This is not what the README file in the 1.6.7 "images" directory says:
"Note to upgraders: as of MediaWiki 1.3, the images used in the user
interface have been moved to stylesheets/images."
I suggest this is changed to something like:
"As of MediaWiki 1.3, the images used in the user interface are no longer stored
in this directory. For MediaWiki 1.3 they are stored in "stylesheets/images",
for MediaWiki 1.6 they are stored in "skins/common/images". If in doubt, the path
used for $wgLogo in the LocalSettings.php file will tell you where they are."