My understanding of reproduction rights is that it depends on where you obtained the image - if it is reproduced from one in the Gwynedd Archives collection either by them or someone else, then it is their copyright and you need their permission. If, however (and its a big if) you have access to an original (even if its the same as one held by the archives) then you can reproduce images of that subject to agreement with the owner etc, and Gwynedd Archives are not involved.
This is the case, for instance, with images from "Caban" - Gwynedd Archives certainly have copies, and even original negatives from this, so images produced from those are their copyright, but if you have access to an original then the image from that can be reproduced without reference to them.
I know Dave Sallery's site uses GA (Web) images with their permission, so as long as the source is stated and GA's permission is sought, I don't think there would be a problem... this does NOT mean that a photographic or photocopy image of an archive item can be scanned in and reproduced on the web, however, as that would be clearly a breach of the terms under which GA supply photographs or photocopies.
Grahami
Grahami
The map is the territory - especially in chain scale.