Size, format, and file size requirements are the same for digital images as scanned images, but resolution works a bit differently on a scanned image than on a natively digital image, as a scanned image can only ever be as clear as the resolution of the original print.
Scanners that use dpi (dots per image) Instead of ppi
Here are some general formulas you can follow that should work:
If the image you are scanning is at least 5 x 8 inches (each dimension must be at least that size) and no larger than 10 x 17, you should scan at 300dpi.
If either dimension is smaller than 5 x 8 inches but is at least 2.5 x 4 inches (examples: 4 x 6 or 5 x 7), you should scan your image at 600dpi.
If your image is smaller than 2.5 x 4 inches, you should scan your image at 1200dpi.
If your image is larger than 10 x 17, you should scan at 150dpi.
The above guidelines are designed to make things easy and to, hopefully, always work, but that doesn’t mean that no other settings will ever work.
If you have already scanned an image at any dpi, and it shows on your screen as at least 890 x 450px and no more than 1800 x 900px without you having to enlarge it on-screen, you don’t need to rescan your image. The image will work on our website.
A Note About Scanners
Many scanners will translate dpi (dots per inch) into ppi (pixels per inch) well. If your scanner offers a ppi option, try it and see if the images come out at the correct size. If you are using a scanner that only has dpi or if you are selecting the correct ppi and getting photos that aren’t large enough, some calculations need to be done, and the above should help.