Since the pixels are square, the edges of features in the image will have a stair-step appearance. The more pixels and shades of gray that are used, the smoother the edges will be. Images that have blocky or square stars suffer from undersampling . That is, there aren't enough pixels being used for each star's image. The CCD user has some control over focal length and pixel size.
Telescopes come in various focal lengths, and focal reducers can be utilized.
Similarly, CCD cameras come in a variety of pixel sizes. The KAF-1000 and SITe cameras have 24 pixels. Unfortunately, we don't have as much control over the size of the star image, which will vary, depending mostly on the seeing conditions of the observing site. A good rule of thumb to avoid undersampling is to divide your seeing in half and choose a pixel size that provides that amount of sky coverage. For example, if your seeing conditions are generally 4 arcseconds, you should achieve a sky coverage of 2 arcseconds per pixel.