Check out this API instead.
but I myself am trying to look into this, and I do not see a clearly documented V3 means. I see ways to use the V2 and V3 APIs together to achieve this, but I'm hoping that this is just a story that needs to be fleshed out for V3 that just isn't documented yet. Stay tuned, and we'll see what we can pull together.
Actually, I a colleague gave me the answer and I completely spaced on this one. See this thread:
Basically you send a multi-part request to the API with the image file definitions to upload and you are good to go. I'm going to see if I can pull together a better canned example for you, but this should get you started in the right direction.