To copy photos between libraries, just select them in one library and drag them to another. iPhoto Library Manager will open the other library in iPhoto and copy the images along with their metadata to that library.
Merging libraries is also quite easy. Click Merge Libraries in the toolbar and an entry of the same name appears in the iPhoto Libraries pane. In the setup area to the right, you add your source libraries and either merge them into an existing library or create a new, empty library as the destination of the new merged library. In the process, iPhoto Library Manager can look for duplicates; the utility lets you choose which of the duplicate images to add to the library--the original unmodified version, for instance, or an edited version. To see what the merged library will look like prior to committing to it, click the Preview button in the top-right corner of the window.
So far, so good. The Find Duplicates feature deserves more attention, however. It works using an algorithm designed by the application's developer. Once duplicates are identified, you can then filter them using rules similar to rules you might construct in Apple's Mail. For example, you can select photos by constructing a combination of such conditions as rating, file size, description, modification date, and title. In an actions area you then choose what to do with those images filtered as duplicates--for example, move them to iPhoto's trash, assign a keyword to them, or move them to a Duplicates library that iPhoto Library Manager creates.
This is very helpful, but in my testing, the algorithm that initially identifies those duplicates is only moderately effective. It's fast, but it failed to turn up quite a few duplicates I had in one of my libraries. While I'm happy that the feature exists, I'll continue to use Brattoo Propaganda Software's $8 Duplicate Annihilator, which can take hours to scan a large library, but produces better results.
Still, that gives us one just-okay feature among many very good ones. Considering that iPhoto Library Manager truly provides the power for those with tens of thousands of images to manage multiple iPhoto libraries, I consider that more than fair.
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