You don't have to jailbreak your Kindle, or render images. You can just point its web browser at any webpage you design, and disable the Kindle's "screensaver" (its ads or sleep screen) with debug commands [1, 2]. You'll be stuck with a browser bar along some edge of the Kindle (you can rotate the device orientation to put it at the bottom or right edge), but it's a small price to pay for being able to write your wea…
It would be even cooler if Amazon also encouraged and built a "Kiosk mode" browser view of the kindle for this sort of display hacking.
Like I totally understand why they wouldn't for new Kindles, since I assume part of their ebook sales help subsidize the hardware, but if they enabled it once a device hit 5 years old or something, I don't see what they'd have to lose.