What type of image do I need to provide?

Please provide a very high file format, clear, non blurry, non pixelated, photograph that you would like painted. What I need are large enough images that the details of a person's face and/or other features you'd like included in the piece (hands feet, shoulders, etc.) are readily visible, and in sharp focus. If the image is emailed to me, the resolution will have to be strong enough that when I print it, all details are visible and focused.