How do I share full-resolution photos between Apple devices? As the title states, I need to know a way of sending full-resolution photos from one Apple device to another (iPhone to iPhone/iPad/Mac) but don't want to lose quality at all.

I'm guessing photos get downsized in iMessage. What about AirDrop? What about sharing a photo album via iCloud?

Does anyone know the definitive answer?
Airdrop sends full sized versions.

iCloud link/album sharing sends full size versions.

iMessages can downsize if enabled in Message settings, but I don't know otherwise. 

Put them in a note and add collaborators or create a sharable link.

Put them in iCloud Drive and share from there.

Use Dropbox, Firefox Send, Google Drive, OneDrive.

Plug in the iPhone to a Mac, trust the device and import using Photos.app. And then export unmodified original or let it do so modifications.