Support uploaded images

[relativesanity]

I'd love a way to embed images in my articles that are uploaded into a relative directory.

Articles get cached in memory for serving when they've been sucked in. We need a similar flow for images:

• get images (Dropbox, file storage)
• cache images for serving (file storage, s3)

I know Dropbox can serve images, but does that not need to be set explicitly by the user? Can the API enable web sharing on a directory under its control?