How to back up iPhoto to a 3rd party provider

There is no online provider than can backup an iPhoto library and successfully restore it in working order. The library must be on a volume that is formatted OS X Extended (journaled) in order to preserve its complex ecosystem of database files, links, file permissions, etc.

You can export all of your your original files to folders on your hard drive and then upload them to an online storage system. That will backup your photos but will lose any of your edits and organizational efforts. Use these export settings:

Otherwise, if you want to be able to retrieve a working library use an external HD properly formatted or use Time Machine and an EHD for your backups.

I am sorry to say that I must concur with you about the failure of online backup with iPhoto.

I would also like to include that in my testing of online backups, it also proved true that they are incapable of restoring your library if it is created with Aperture.

I can't say this for a fact but I suspect that the same is true if your library has been created using Photos.

While your solution to backing up the photos without adjustments, EXIF data and organization may be possible, it is certainly not something I would want to even consider as my backup solution for my photos.

I can't say this for a fact but I suspect that the same is true if your library has been created using Photos.

Definitely so.

Found addition info on that in this Apple document: Updating from iPhoto to Photos for OS X - Apple Support

If you store your Photos library in a location that's part of a cloud service (for example, Dropbox, Box, or Google Drive), your library might be damaged by the syncing process. As a result, you could lose photos.

To see your photos on all your devices, you can use iCloud Photo Library. To back up your library, you can use Time Machine.