Using screengrabs not only allows you to select exact images but also provides a good defence for publication (under fair dealing or fair use), as opposed to published stills, which are stand-alone creative works i.e. you are quoting from a work rather than reproducing a work in full

Great news for many, but there's nothing wrong in paying for the BNA if you can. It's what enables more British Library newspapers to be preserved through digitisation, benefitting everyone