[vidarh]

Copyright already has a lot of limitations. It has never been, nor been intended to, be absolute, because the point is to promote the arts and a too strict grant of rights would stifle it instead - indeed most places it is accepted that copyright is a significant limitation on the liberty of society at large, justified (or not, depending on ones opinions) by encouraging more works, but accepting it as a restriction means there is some degree of acceptance that it should not be more expansive than it needs to be (and many will disagree about whether the current length of copyright is or is not more expansive than it needs to be)

The only limitation that needs to be there for training on copyrighted works not to be infringing is to accept that extracting information about the work is not infringing if copyrighted elements of the work itself is not significantly reproduced.