It seems that Apple has introduced a new addition to have the ability to upload photos to the cloud directly from the iCloud.com beta web service, although yes, indeed you have to be registering as iCloud beta program member (beta.icloud.com), in order to have access to it. I have proceeded to check it and I see that I still do not have this option activated, although I do not think it will take long to activate it.
Specifically, before we could only consult our photo albums or moments, to later select the photos and in this way delete them permanently or download them to our Mac. Now with this ability to upload photos from our computer, we can also include images that have not been strictly taken with an iOS device or that we have received on it, but can come from any source.
The operation is very simple, as I mentioned, a button will appear next to Select Photos to Upload images where a Finder window will obviously open from which we can select the photos we want and that once loaded in iCloud these will be synchronized in all our iOS and Mac devices where we are logged into the service, likewise other devices would also be capable of synchronizing with the images thanks to the option to share iCloud photos, »ICloud Photo Sharing». Although yes, the option for video files is not available as if it is on iOS, so the management capacity on our part is reduced to only images.
Surely this is a small appetizer or prelude to what awaits us, that is, Apple has already confirmed that it would stop supporting iPhoto and Aperture during this year so we will surely see New applications for next year with a renewed interface and more possibilities added with options linked to iCloud.