A good general rule is that if you intend on enlarging the photo, add 1,000 ppi for every 70% enlargement.

• 300 ppi: If you are going to have the image printed the same size as the original image
• 600 ppi: Great for making a print the same size as the original or increasing the print size by 50%.
• 1200 ppi: If the original is going to be enlarged by more than 200% then this is recommended. Also, for images that are going to have restoration work done on them it is best to be scanned at this resolution.