In short, restoration is not a mechanical process. It requires a great
deal of judgement and artistry. This judgement and artistry is used to
try and repair things in a way that fits in with what existed. This is
why restoration is generally *not* done on one-off, deliberative works
like paintings for commons, but lithographs are a semi-randomly
created process, where etching by acid creates random pits, and the
amount of these pits determines the darkness of that part of the
image, and there will be some variation between copies due to amount
of inking and paper variations. In these gaps, you have enough freedom
to do a restoration, but, outside of the basic stuff like "remove ink
blotches from the white space", there's a necessary level of creative
decision making to decide how to repair. To give obvious,
easy-to-understand examples:in my restoration of Left Hand Bear, where
the corners had been irregularly cut off to round them, in a very
uneven, untidy way. I had to reconstruct those areas, including fixing
some damaged text (Luckily, the LoC notes told me what it should say),
and, on one corner, I actually had to fake some water damage to avoid
misleading the reader by providing fine details about the sleeve that
didn't exist.
Another good one was my Women's Suffrage restoration, where a big
chunk was simply missing, and I had to recreate the shoulder of a
dress and other incidental details, without which the eye would be
immediately drawn to the damage, and away from the actual image.
I try to be fair with this. If I've done very little, I explicitly
note this. If you want to say that my Quick and Easy restorations
folder should be considered PD, I'd probably agree with you, in fact,
I believe I've said to consider them PD. But there's a logical fallacy
called the False Continuum: the idea that because there's a fuzzy area
in the middle, there can't be clearcut cases on either end. That seems
to be getting used to argue that no amount of work can ever gain a
copyright (in explicit violation of the text of the PD-scan policy).
Note that that policy also points out that the amount of artistic
decision is very low in the UK.
Commons can deal with ambiguity. For instance, very simple logos can't
gain copyright? How simple? We don't know, so the bar of how simple is
simply set at a point sufficiently low (text, geometric shapes) that
it's clear cut, which lets Commons benefit from the policy, while
still staying well away from anything that can get us in trouble.
-Adam Cuerden