You can turn on My Photo Stream for the same iCloud account on more than one Mac. When you have My Photo Stream turned on for more than one Mac and you upload a photo to My Photo Stream, the upload includes the event information from iPhoto or the project information and hierarchy from Aperture. If the receiving application has Automatic Import turned on in iCloud preferences, the event or project information is passed along in one of the following ways:
Photo uploaded from iPhoto on one Mac and pushed to iPhoto on another Mac: If the iPhoto library the photo is pushed to contains a duplicate of the event in which the photo originated, the photo is placed in that event—even if the event has been renamed. If the same event doesn’t appear in the iPhoto library the photo is pushed to, a new event is created and named after the photo’s original event.
Photo uploaded from iPhoto on one Mac and pushed to Aperture on another Mac: A new project is created in the Aperture library and named after the iPhoto event in which the photo originated.
Photo uploaded from Aperture on one Mac and pushed to iPhoto on another Mac: A new event is created in the iPhoto library and named after the photo’s immediate parent item in the Aperture library. For example, if the photo originated at the top level of a project named “Travel,” a new Travel event is created in iPhoto. If the photo originated in an album named “Christmas 2011” that is inside another album or a project, the new iPhoto event is named after the Christmas 2011 album.
Photo uploaded from Aperture on one Mac and pushed to Aperture on another Mac: If the Aperture library the photo is pushed to contains a duplicate of the project or album in which the photo originated, the photo is placed in that project or album—even if the project and any subordinate folders and albums have been renamed or restructured. If the project or its albums don’t exist in the Aperture library the photo is pushed to, the project hierarchy is replicated and the photo is placed in its original position.
Note: When pushing photos to iPhoto or Aperture, iCloud downloads photos to iPhoto events and Aperture projects that have universally unique identifiers (UUIDs) matching those of the photos’ original events or projects. If you manually create iPhoto events or Aperture projects with the same names as events or projects in other libraries, those events or projects are not recognized as matches. To create matching events or projects, you must copy them from one library and merge them with the other.