. What does the raw moment m00 represent for a binary image?
m00 = sum I(x,y) over all pixels, which for a binary image is just a count of foreground pixels.
. Why are central moments mu_pq preferred over raw moments m_pq for describing a shape's spread?
Raw moments (except m00) depend on where the shape sits in the image; central moments are translation-invariant.
. What property makes Hu moments useful for comparing shapes?
The lesson shows a translated and a rotated+scaled version of the same shape produce similar Hu moments, while a different shape does not.
. The orientation formula theta = 0.5 * atan2(2*mu11, mu20 - mu02) is computed from which moments?
The second-order central moments describe the shape's spread around its centroid, from which the major-axis angle is derived.