HTML5 when implemented is supposed to interact with the system's clipboard. I imagine the following scenario would work:
- paste the image data from clipboard to canvas
- get the canvas pixel data back as an image using
toDataURL(): see Canvas2Image
- upload the image to server when submitting: see Saving canvas image with PHP
Until HTML5 copy/paste drag&drop is implemented, you'll have to rely on Flash or a (signed) Java applet to interact with the clipboard.
I would *love* to get this working with our editor. While I love skitch, it could be even easier to paste direct.
Though right now we do support pasting of image URLs (we download them properly to avoid hotlinking) -- and we're working on HTML5 drag and drop support too.