https://frankl.in/code/process-icloud-photostream-in-real-time

icloud_photostream.js

// Only copy new images to another folder:
require ('osx-photostream') ('~/Pictures/iCloud');

// Do more stuff with them:
var ps = require ('osx-photostream') ();

ps.on ('update', function (file) {
    console.log ('New image added: ' + file.filename);
};)

// Or do both and first copy to another folder,
// then tell another app a new image is ready using AppleScript.
var ps = require ('osx-photostream') ('~/Pictures/iCloud');
var exec = require ('child_process').exec;

ps.on ('copy', function (file) {
  // Forward image to friend
  exec ('osascript -e "tell application \"Messages\" to send POSIX file \"' + file.copypath + '\" to buddy \"friend@email.tld\" of service \"E:my@email.tld\""');
});