See
JavaPasteAddOn
We wrote this to provide the ability to copy a picture onto the clipboard and paste it as an attachment to a page. As a side effect of the implementation you can also copy a set of files onto the clipboard and upload them.
We wrote this as a Java applet. Because the applet accesses the system clipboard, in many corporate environments it needs to be signed. The code to do this is included.
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MartinCleaver - 20 Jan 2002