Yes, I also find this discussion:

http://stackoverflow.com/questions/6333814/how-does-the-paste-image-from-
clipboard-functionality-work-in-gmail-and-google-c

There is some suggestions in javascript this sound for me promising.
Q:"With HTML 5 features(File Api and the related) - accessing clipboard 
image data is now possible with plain javascript."

But I have no mutch expirience with JS.