What are the best settings for e-mailing or printing digital pictures?

In general, if you are e-mailing the pictures to friends who
will view them on a computer screen, you will want to send
them pictures in the jpeg format at 640 x 480 pixels. If you
are printing the pictures, you need about 150 pixels per inch
of print size. So you would not want to print your 640 x 480
images at a size bigger than 4 x 3 inches.

Cameras can be quite complicated and use unintuitive jargon.
Your camera probably has several different picture quality
and picture size settings. For example, we'll go through all
of the quality settings of one of the cameras we use. We took
the same picture in all of the different modes and here are
the results.

Setting Name Format Quality Pic Size (pixels) File Size
TIFF TIFF No Compression 2048 x 1536 9,231 kB
SHQ jpeg 97% 2048 x 1536 1,391 kB
HQ jpeg 91% 2048 x 1536 682 kB
SQ1 jpeg 87% 1280 x 960 249 kB
SQ2 jpeg 73% 640 x 480 62 kB


Quality
Most cameras store the images in jpeg format. This is
a compressed format that reduces the file size of the images.
Some cameras also have an option to store the pictures in
an uncompressed format (like TIFF). Generally you will want
to use the jpeg format because the uncompressed pictures will
quickly eat up the storage space on your camera. There are
different levels of compression for the jpeg format. Some
cameras will have good, better, best setting. These settings
can be equated to a quality level parameter of jpeg
compression. If the quality level gets down into the 60
percent range, you might start to notice little squiggles and
extra graininess. The graphic below shows the relative
picture quality and file sizes for different jpeg quality
levels.

Size
The picture size is usually adjustable too. The picture size
is measured in pixels, so you need to pay attention to how
many pixels wide and high the pictures you take are.
Generally, a computer screen is 800 to 1200 pixels wide, with
800 being the most common setting. If you are e-mailing
someone a picture that they are going to look at on their
screen, then there is no reason to send them a picture bigger
than their screen. Many cameras take pictures at 640 x 480
pixels, which is a good size for viewing on a screen. For
comparison, the largest photos we use at How Stuff Works are
about 400 x 300 pixels.

For printing, the general rule is that you want 150 to 200
pixels per inch of print size. On this page, Kodak recommends
the following as minimum resolutions for these different
print sizes.

Print Size Megapixels Image Resolution

Wallet 0.3 640 x 480 pixels
4 x 5 inches 0.4 768 x 512 pixels
5 x 7 inches 0.8 1152 x 768 pixels
8 x 10 inches 1.6 1536 x 1024 pixels

On our camera, the SQ2 pictures are perfect for e-mailing.
The SQ1 pictures are good for printing at 5 x 7 inches, which
is nice because you can get two pictures onto a single sheet
of 8.5 x 11 paper. And the HQ, SHQ and TIFF settings all make
nice full-page prints. But you can see that the file size of
the biggest images quickly gets too big to e-mail.