PicBackMan’s Dropbox uploader for Mac is easy to use tool to bulk upload, bulk download and migrate Dropbox photos to any other specified online service or cloud account. Using PicBackMan for Mac, you can effortlessly backup your entire iPhoto (Photos) collection. The automated program will keep a check on any new addition of the photos in your iPhoto (Photos) folder. As soon as it finds new photos, they will be automatically uploaded to your Dropbox account.
PicBackMan is a free photo/video uploader that helps you to keep your memories backed up to your favorite online services.
Users in 130+ countries have backed up.
... an excellent job of uploading more then 300GB of photos to 2 different services