Scanning/photocopying vs. photographing the material
Consistent even lighting moving with scanner will give even illumination across the full scan. No vignette effect.
Lens distortion - particularly at the edges. Scanner head is a line-scan camera with each pixel vertically aligned with the subject.
Physical depth. Scanner is very shallow.


Try it yourself with a camera and a flat printed page. Look for evenness of tone across the page. Try it with squared paper and see if the lines are straight in your photo.