any previous posts from you. Your profile shows just this one post above.
I've just typed the whole of the below, but have now re-read your post and see I am on the wrong tack.
If no-one knows the locations of the lighthouses in your Desktop Background theme, then no-one knows.
Anyway, here's what I originally said;
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I don't see any lighthouse scenes in my own Windows 7 Ultimate Desktop Backgrounds or Screen saver options, so I doubt what you saw was supplied by Microsoft. However, I didn't look through all of the themes offered by Microsoft at;
http://windows.microsoft.com/en-GB/windows/downloads/personalize/themes
There may be some lighthouse scenes available there.
If not, then how about making your own theme? Using Google images (or your favored search engine if different), search for Lighthouse 2660x1024, (the numbers are may screen resolution, so yours may be different). Save them to your Pictures folder with the owner's permission, then use those for your own desktop background theme.
Mark