I would *not* delete the photos from your hard drive. The backup service allows you to restore the photos in the event of a problem locally. Deleting them locally will remove them from the backup on the next cycle.
Furthermore, the service, as well as OneCare itself, is at end of life. At the end of your subscription you will need to download any photos from the service that you need to restore as the online copies will be deleted. And, you'll need to remove OneCare,
too.
See this post for End of Life information for Windows Live OneCare -
http://social.microsoft.com/Forums/en-US/onecaregeneral/thread/81996436-edad-41ba-bdfc-02fc094e2ca9
-steve
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