I discovered it's an MTK chipset when it ignored the non-MTK GCD file I fed it. The HWID is 1091 and Part Number is "006-B1091-00" in the GarminDevice.xml file. It does seem to be EU flavored because there was an SD card in it when I got it that contained an EU map database.

Thanks for the replies. I don't know this Nuvi's history or how it came to be showing the photo in place of the logo, or why selecting a different photo in the "Picture Viewer" replaced the orginal photo with a blank screen and no logo. Flashing it to restore the logo seems more risky than it's worth.