Whenever you capture a photo on your iOS devices, a copy of the photo is saved automatically into Photo Stream, which is an iCloud storage of your last 1,000 photos. You can access Photo Stream on your Mac by launching iPhoto or Aperture.
Turns out that all your photos in Photo Stream is saved into a folder on your Mac, and an alternate way to access them is via Finder.
The folder location of Photo Stream on your Mac is at:
From Finder, click on Go menu and press the Option key. Select “Library” from the menu, and navigate to folder Application Support > iLifeAssetManagement > assets > sub.
Here you have it, all your photos in Photo Stream are located within this folder, with each picture under a folder with long unreadable name.