There are several ways including free and paid, but I will show you the free way.
- Google has announced new Google Photos that works with Google Drive, so you need to make sure that there is a Google Photos folder in your Google Drive.
- Head to www.multcloud.com and register an account.
- Confirm the accounts and start linking your cloud services
- Click Transfer on the header of the website and select the folders you want to transfer. Your destination folder should be Google Photos.
- Boom! You're done!
Let me know if you caught any issue.