This issue has been covered in different degrees in various places around the net. One of the most cogent observers has been Jonathan Bailey, in his articles ‘Is Flickr Letting Down its Users?’ and ‘Why Flickr Licensing Fails’.
The basic problem is this: some third-party websites and applications have been using the Flickr API or feeds to publish photographer’s images in ways those photographers did not intend or allow. Photographers familiar with the relatively clear licensing interface of the Flickr.com website have been surprised to learn there is a ‘back door’ into their carefully-licensed images.
Some photographers reacted by stating that they did not intend their photo to appear in any form other than the original: in the HTML pages of the Flickr.com website. A few feel their only choice is to quit Flickr, or even quit the public Internet, moving their images to private domains they believe to be safer for their property. These drastic, reactionary moves are unfortunate, but understandable. The technical situation is complex and facts are few.
As a photographer, developer, and Flickr user, I decided to investigate the problem from a technical point of view. (Jonathan Bailey and others have already put forth good arguments for more ‘soft’ improvements in Flickr’s licensing model.)