Historical note: this was written in 2001!
How good is "good enough?"
Important term: the pixel is the smallest bit of image information you can resolve. One pixel is a single point on your computer's monitor.
Older computer monitors are usually set to a display resolution of 480 pixels high and 640 pixels wide. This picture size is often called VGA.
Today many computers are set to a resolution of 600x800 pixels, while professional graphic artists may choose an even higher resolution..
Choosing the right digital camera is easier if you know why you want it. What will you be doing with the pictures you take?
Why send somebody a picture that won't fit on their monitor? A picture that is bigger than VGA (480x640 pixels) won't fit on the oldest computer monitors. It will fill up more than 3/4s of the screen on a typical monitor set at 600x800 resolution. Therefore, for web-sites and e-mail anything more that VGA resolution is overkill.
Scrap books and genealogical records usually are printed on inkjet paper, and it's nice to throw in an occasional photo. A VGA image will make a pretty good 3"x4" photo when printed on a good paper.
Photo quality images are another matter. While some printers have settings of up to 1440 dpi (dots per inch) for superb photo rendition, that doesn't directly relate to the size of the image file that is needed for good results.
After looking at an awful lot of images, I've come to the conclusion that a resolution of 135 pixels or more per inch is the minimum for images to pass as photographs.
Having carefully calculated that, I must admit to having made images bigger than the above "maximums" that look pretty good. Using Adobe PhotoShop and resizing the images to increase the pixel count lets you make sharper images, but that can't replace detail that's not in the original photo.
The larger the image is, the larger the file becomes. A 960x1280 pixel image makes a file 4 times bigger that a 480x640 pixel image. Bigger files require more storage space on your computer and take longer to transmit/download/e-mail than smaller files. Your friends will not thank you for e-mailing them a picture that takes ten minutes to download!
File size is dependent on two factors:
That's one of the toughest questions you can ask. The bigger the capacity of the card, the more files it can store. The bigger the files, the less you can store. As an example, with an Olympus C-3000 using a 16MB card, you could store this many files (we left out some possible combinations)