The photos come courtesy of XDA Forums member dr.guru who claims that the prototype doesn't boot because it's been remotely wiped by Google. The leaked photo's of the fastboot screen shows that there's "no valid slot to boot." you can also see the phone's nickname is crosshatch, and that it has 4GB of RAM and 64GB of storage.
The logo on the back is used by Google for engineering units with the barcodes and identifying stickers. The back of the phone is rumored to be all glass with top part glossy and bottom part matte, a single part of glass. The notch looks to house the dual front facing cameras.
Source: XDA Developers