The Merge Process

1. The source library is opened and all necessary information is gathered from it.
2. The destination library is then opened.
3. Each album that was in the source library is recreated in the destination library. If the "Combine albums with same name" option is enabled, then if the destination library already has an album of a given name, that album is used instead of a new one being created. In iPhoto 6, support was added for having multiple albums with the same name in a single library. If there is more than one album in the destination library with a given name, then preference will be given to one that is in the same nesting of folders as the album in the source library. If no such album exists, then the first album with the name in the library will be chosen.
4. Each roll/event from the source library is then imported into the destination library. After the photos are imported, each photo's metadata and the original version of any modified photos will be restored, and, for each album it belonged to in the source library, it will be added to the corresponding album in the destination library.