My question about You Tube broadcasts is more to the question as to when extraneous elements -- the shaky photography, extremely oblique angles, the occlusionary shadows -- add a value and signature, albeit unintended, that creates a new original. Juan Gris repainted several of Cezanne's paintings, faithfully following the original compositions, but his own style flattens some aspects of the original and gives an very un-Cezannean elegance to others and creates a new work of art. Ann Barzel's films certainly bear her signature. It seems that at some point that such "degraded" videos are no threat to the owner or trustee of the original choreography.
You've perhaps answered this in your example about removing the scratches (though here it's the equivalent of generating them).
Actually, I haven't. What you're talking about is the transformational aspect of the use, which is the first test of fair use (http://fairuse.stanf...apter9/9-b.html). The big case study these days is the famous Shepard Fairey Obama "Hope" poster, which was based on a photo from the AP. Although a verdict wasn't/hasn't been issued, it wasn't looking good for Fairey.