I've never seen a larger image of the screenshot of the DK portrait in Banjo's house, but I feel like I've seen one that is slightly better quality than the one posted here. I also remember it being featured on an RWP page about BK beta content from at least 2003 when I joined the forums.
Since the speech bubbles are at a slight angle, my best guess is the source is a magazine or possibly even a photo of a TV from a convention demo. (Magazine or other print source seems more likely, mainly because the colors look like what could be produced by CMYK rather than RGB.)
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