This image of Castell Coch is from Amgueddfa Cymru – National Museum Wales. The photograph is mounted on card along with shots of a T.V.R. Converted Bristol Class locomotive and Barmouth Bridge under Cader Idris.
The photographs aren’t dated unfortunately. After some quick research of Barmouth Bridge though, it turns out the drawbridge in the photo was replaced by a swing bridge in 1901. If the photographs were taken by someone on a tour of wales in the late 1800s, I think it’s fair to assume the photo of Castell Coch is of a similar age. I have some Edwardian postcards that feature the same view of the castle and the scenery matches.
Then and Now
The most obvious difference is the number of trees along the moat and on the grounds in front of the castle. The grounds have stone edging and vegetation among the trees.