Imagine person A sharing a photo on a website publicly, for example on a community site like Flickr. Next, person B "pins" this on a board in Pinterest, without asking for permission. The same photo is now visible in Pinterest.
What are the legal implications of this? My understanding is that even on a public website, photos are copyrighted (unless otherwise stated by the photographer) by default, and for republication, one must ask for permission at the copyright owner.
Is pinning an image considered a republication? Does it require permission? Or is it more like embedding, or a fair use that does not require permission?