In the old days, you dropped your film off at the drugstore and waited to see your prints. Then you paid for them all, got them back, threw out the bad ones and went back to order reprints. With digital cameras and online services, the process is reversed. You see your pictures first on the camera or computer screen, and then only send the best images for printing. There is no waste, and you can order as many copies of just the ones you want, in the sizes you want, all in your first order.
Online services use technology that goes far beyond anything the average home user can acquire.
The digital image is beamed onto real photographic paper and processed like a film-type print. This gives the highest resolution possible, the widest dynamic range and print life comparable to film-photo prints. The prints are also physically more durable than water-based inkjet prints you might produce at home. The first thing is to make sure that the image is the right size for the print or enlargement. Most users will also use software to enhance the image.