how to share photo libruary between macbook and imac

What do you mean by "Sync".

The general term means when two Libraries (A and B) are compared and files in Library A are copied to Library B, while files in Library B are also copied to Library A so that both Libraries are identical.

This is bi-directional copying and you cannot do this automatically with iPhoto. No Syncing software is capable of parsing the iPhoto Library in this manner. One or both of your Libraries will be damaged if you try this.

You can have uni-directional copying - files in Library A are copied to Library B - this is essentially backing up. Obviously you can also copy from Library B to Library A.

The nearest you can get to syncing is to use iPhoto Library Manager to move files/Albums/Events plus associated metadata between Libraries. This process cannot be automated.

There is some software that may do what you want. However, it only copies and imports those photos in LIbrary B that are not in Library A into A and those in A that are not in B into B. The keywords, titles and other metadata and original orginatizaton is not kept. The photos transferred are all in one Event.

You can check it out here: Sync iPhoto libraries | SyncPhotos (formerly iPhotoSync) | Haystack Software

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