What? Ok, I take back the "like YouTube." How about like Google search? Users don't spend 3 mins on google results page. Also, a text ad can be targeted to whatever tags the pic has (ie: New York hotels).
Over at YouTube, users are willing to sit through 15 seconds of pre-roll ads so they can watch 3 minutes of whatever. Revenue is generated.
If a user arrives at Flickr, they've probably already found what they're looking for. Someone searching who arrives at a Flickr page of dolphins will see pictures of dolphins and have succeeded in their task. There's not much chance they'll notice any ads Flickr shows and click because they want NFL tickets.
I'm not saying Flickr should go down this road, but you're wrong in suggesting that sites can't make money from adverts unless they are pre-rolls or on search engines.