1: the unsplash photo has higher visual quality, as it was likely taken with by a professional photographer with equipment in a controlled environment, as opposed to my picture taken randomly with a phone camera.
2: The scans have a higher contrast, are perfectly vertical, and despite smaller file size and resolution, appear to be higher quality.
3: the simplest way to improve quality is better equipment (camera or scanner). For photographs, lighting could also be adjusted, for example the left-most coin is reflecting light, and it is hard to tell what coin it is.