Hi Richard,
Welcome to RootsChat and I hope you continue to enjoy us/it in all our aspects

Copyright is a thorny theme, and the Copyright Editors will willingly tell you more, but as I understand it, the problem is
not in reading an image and passing on the information
on the image, but in passing on
other people's transcriptions of the image.
As you so rightly point out, the data and images are Crown Copyright and RootsChat also insist that this fact is mentioned in all relevant postings.
You as a private person are allowed to read the images and copy (transcribe) what you see,
on the imageA commercial company can also transcribe these images and make lists of the transcribed data (
indexes), which they then sell (CDs, pay-per-view, subscriptions, etc).
These indexes are the
copyright of that company. If you copy their indexes, then you are violating
their copyright, and this is what RootsChat is warning about.
However, althought the
index is company-copyright, the
image isn't, it is still Crown-Copyright. So if you see the image on a commercial site or on a CD you have bought, you are still allowed to look at the
image and write down what you see on the
image, as this is still Crown Copyright, with the aforementioned conditions of use.
In other words, you can make your own transcriptions of an
image, but
never, never copy a commercial company's transcriptions (
index) of the image.
Hope this helps, but if you would like more guidance, then you can always ask the Copyright Editor.
The more people know, why we handle as we do, the less need for us to handle !!
regards,
Bob