Backing up Photos library (located on an external hard drive) to iCloud

Hey everyone,

I recently had a (costly) data recovery situation and want to start using iCloud to back up my computer, but mainly my photos library. The problem is that my photos library is currently located on an external hard drive (WD 1TB My Passport), and is far too large to move back on to my mid-2015 Macbook Pro.

Are there any workarounds for this? Would a different type of external hard drive allow me to keep the photos library off my computer while still backing up to iCloud when connected?

Alternatively, if I was able to temporarily relocate my photos library to a friend's computer, log in to my iCloud account and back it up, and then remove the library from his computer, would the photos remain in my iCloud? If so, would I only be able to access them through the iCloud web browser, or would those photos also appear in my Photos OSX application where I can use all of the different functionalities (locations, facial recognition, etc.)

Any help would be greatly appreciated!