How does the carousel image work on the camera device types?

I have been looking at the camera device type handlers and I can’t work out how the images gets from S3 storage to the carousel.

The various apps all seem to end in a save method which puts the image into storage with a seemingly random filename, the image then miraculously appears in the carousel.

How does this work?
The carousel seems to use the attribute device.image, where does this get the images from?

Any advice would be appreciated?!