iCloud: Add photos to Photo Stream manually
You can manually add photos from iPhoto, Aperture, or the Windows desktop to your photo stream. You may want to do this if you’d like to add photos that don’t appear in your photo stream automatically.
From iPhoto or Aperture
From your Windows desktop
From your Windows desktop, drag any photo to the Photo Stream Uploads folder you chose in the iCloud Control Panel.
For a list of file types that can be added to Photo Stream, read “What photo formats does Photo Stream support” in the Photo Stream FAQ on the iCloud Support website.