Obviously the more you enlarge a pic the less clear it becomes and photocopies are not great quality to begin with.
Rather than trying to crop out individuals, it is better to do this at the scanning stage. When you scan, most scanners have a 'preview' facility where you can select a specific area to scan. Select your individual and scan it at the highest resolution as a png or tif file. This is the best result you are going to get from your source image.