You can't increase the resolution of an image.However, you can increase the DPI (dots per inch) while decreasing the size of an image to make it suitable for printing. It really depends on the quality of the image taken with a digital camera - most modern phones and cameras should give you sufficient resolution to print at 300 or 600DPI.If you've got a printed photo, then you can scan it at 600DPI (or higher) using just about any £20+ home scanner.
Ed Saper ● 1955d