entry().field('pictures') returns the array of file paths, but not the captions.
e.g. before running the action i have image A with caption 'A', image B with caption 'B'. My script.action adds a new image C to the front.
Then I have image C with caption 'A', image A with caption 'B', and image B with no caption.
If I can get and set the captions then I can stop this from happening.
(This is part of message from memento google group from some user).