Imagine I want a user to be able to copy-paste a selection of pixels from MSPaint into a browser-based app. Is this possible using JavaScript in any current browsers? Will it become possible in HTML5? If not, is it feasible using something like Flex/Silverlight, or is it simply not possible at this time, and you'd have to save a file and manually upload it?
update: sounds like HTML5 should allow it, but that's a way in the future to be genuinely useful. Some suggestions of Java applets and Flash are mentioned, probably Flash would be preferable since parts of the web-client would probably use Flex anyway... I'd rather not have requirement for Java and Flash in my site.