What is this thin, square-ish object on asteroid Bennu? How big is it?

Question

What could this square thing be? Roughly how big is it? From BGR's Our first up-close look at the Bennu asteroid is a messy one:

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rotated, 2x zoomed, and sharpened. unscientifically:

Answer 1

In this composite of the rotating asteroid you can see that it is not thin, but actually protruding:

^{This series of images taken by the OSIRIS-REx spacecraft shows Bennu in one full rotation from
a distance of around 50 miles (80 km). The spacecraft’s PolyCam camera obtained
the thirty-six 2.2-millisecond frames over a period of four hours and 18 minutes.
Credit: NASA/Goddard/University of Arizona}

It looks like an 'ordinary' boulder.
(You can see several more in that sequence)

Simply comparing the 'height' from the second picture with Bennu's diameter of 492m shows this 'boulder' to be 28 meters high.