Copyright law in the age of the internet is a mess. First, UK and US rules differ. Mark Pearce is your guy in the UK. In the US, pretty much anything published pre '24 is now public domain (that date will roll forward one year every year), unless the holder of the copyright has renewed its rights, which can happen with some newspapers or magazines.
A big issue is damages. Even if there are technical violations of c/r in the republication of older materials, damages are often hard to determine. Mark can give a picture of the UK rules. In the US there are statutory damages (even if there are no actual damages), but to be imposed they require a c/r holder willing to incur the expense of filing a claim in federal court or credibly threatening to do so. In short, even if c/r is violated in respect of older, obscure materials we tend to find interesting, they have little, if any, commercial value. Which means that statutory damages are what you worry about. Those can be real but a party willing to assert them strikes me as highly unlikely in most cases.
All of the above is complicated by our ability to distribute c/r materials to millions of people with the push of a button on the internet. There is little in US copyright law that reflects that modern reality. So, as noted, c/r is a mess with few good roadmaps. There are a couple of, but not many, reported cases to help sort things out. Remarkably, the last round of material amendments to US copyright law were in the late 1990s to reflect that new technology called the 'fax machine.'
Note that I am not a c/r lawyer. The above is what I have picked up on my own. If you have c/r questions, you should consult a specialist. In fact, it would be great if a US specialist chimes in. I would welcome any corrections to the above and get an update on where things stand today.
Bob