When you install Dropbox on your Mac, it will create a dedicated folder i.e Dropbox folder on your Mac for storing your photos, videos and files. To sync iPhoto library to your Mac, you will need to find the file for the existing iPhoto library in 'Picture' folder. You need to download and install 'Dropbox Desktop Application' on your Mac to sync your iPhoto Library with Dropbox. Dropbox is one of the best desktop application available in the app store and it is helpful in file synchronization. Dropbox is an online photo & video backup service.
