Your friend is correct. This is copied directly from the Flickr T's & C's (They are part of the Yahoo Group)
"With respect to Content you elect to post for inclusion in publicly accessible areas of Yahoo! Groups or that consists of photos or other graphics you elect to post to any other publicly accessible area of the Services, you grant Yahoo! a world-wide, royalty free and non-exclusive licence to reproduce, modify, adapt and publish such Content on the Services solely for the purpose of displaying, distributing and promoting the specific Yahoo! Group to which such Content was submitted, or, in the case of photos or graphics, solely for the purpose for which such photo or graphic was submitted to the Services. This licence exists only for as long as you elect to continue to include such Content on the Services and shall be terminated at the time you delete such Content from the Services."