Hey, thanks for your reply.
I just need photos (original size) to be shrunk into another folder. I do this with ImageShrink manually at the moment but it's a tedious process because then the shrunk photos need to be put into a backup folder, as do the original photos, which also needs automating.
I realise now that it's not as simple as opening the ImageShrink app, as that just opens the settings. Manually it's done like this:
That's the key part of the process, the other being similar: "Send" | "Save to Drive".