Can one stream photos to Shared Photostream from Finder on a Mac? I know someone who is considering the possibility of setting up an iPad as a digital photo frame. Ideally, they would use Shared Photostreams to easily put pictures on the device. This is easy for any live-updating of the iPad photo frame, but the challenge comes in with the photo archives taken with a standard DSLR camera.

There are many photos, then, that they would like to easily stream from their Mac computer. Because they don't have a lot of extra space on their computer for a large iPhoto library, is it possible to:


Manage multiple small iPhoto libraries easily, and if so how would they do that?

Right now a number of the photos are on SDs cards. Could they basically convert each SD card to an iPhoto Library and then use that to stream?

Is it possible to post to a shared Photostream from a Mac Finder window?

This would absolutely be ideal. A 3rd party app would be fine. I picture something like the standard right-click -> Share.
You can use iPhoto to add to a Photostream from your Mac.

I have Aperture using mine so I cannot fully test it with iPhoto without switching it off in Aperture. But is should work the same way by importing the images into iPhoto which also allows you to organise them. 

And then using the Share feature to share to iCloud. ( photostream )

The share with iCloud startup dialogue in iPhoto:
 



You can have multiple iPhoto libraries and open any of them as the Library to use by holding down the option/alt   ⌥  key when Launching iPhoto.

You should get a dialogue similar to this:



This means you should be able to import a SD card to it's own Library
Although it maybe easier to just organise within iPhoto and a singe Library



When selecting an image in Finder. The Share contextual menu does not offer up iCloud. So it looks like no with Finder at the moment