I'm looking at the art on the link you provided and my guess would be that it is a print. A reproduction and NOT the original art.
Again this is my guess, but here are my reasons:
1. You can clearly see the large pen signatures of Quesada and I on it. These are in addition to the original signatures on the actual piece of art. If it was the original art, I don't think we would sign it twice like that.
2. I don't believe I signed the original twice.
3. After I sent the art to Marvel, I don't think I recieved it back to have the oppertunity to sign it twice. Joe Quesada and I divided up those covers and we agreed that he would keep that original.
4. If Joe did part with it, as a donation to the charity or otherwise, I think he or the charity would have sold the original for at least $3,000-$4,000 if not more.
5. I do donate prints of many items to the charity, and my guess is that this is one that I donated, and that the charity asked Joe to also sign.
For those reasons, my best estimate is that this is a reproduction and not the original.