Thanks for the comments.

@Minileed - your assumptions about the construction are correct. The pictures were taken outside in daylight (not direct sunlight) against a black piece of mattboard. Once I had the image framed correctly, I add a white sheet of paper to the edge of the frame, somewhere it can be cropped out. This helps the camera to balance the image - without the paper, it seems to think that the lightest thing in the frame MUST be white, and it overcompensates, losing a lot of the subtlety and detail.

I hope this helps.

All the best - Aba.