What's a pixel and how many do I really need?
The Picture Element or pixel is the smallest unit of information on a digital picture file.
very low resolution 12x16
These pixels are lined up in rows and columns. When your picture has enough pixels that you can no longer distinguish them as individual dots, they seem to blend together to make a continuous-tone photograph.
The photo at the upper left has 12 columns of pixels and 16 rows of pixels. Obviously that's not enough for a good photograph - in fact you probably couldn't tell what the subject was!
Multiply the number of columns times the number of rows to get the number of pixels in your photo. A megapixel is one million pixels - a square picture 1,000 pixels by 1,000 pixels would be a true megapixel.
12 columns times 16 rows equals 192 pixels. That's about 1/5000th of a megapixel. And obviously it's not good enough.
1200 columns time 1600 rows would equal 1,920,000 pixels. That's about 2 megapixels.
A photo file 2 megapixels or larger will make very good 8"x10" prints, if no cropping is necessary and the print is made by a professional lab. Printed on an inkjet printer, it probably won't look as good.
For use on a computer monitor set to 600 x 800 resolution, any file bigger than one-half megapixel will more than fill the screen. You don't need anything bigger for e-mail or web use.
Once you've got enough image details - that is, enough pixels - to fill up the screen of your computer, anything else will spill off the edges.
For big prints - 11"x14" and beyond - you'll get better results with a 6 megapixel or larger image size. More megapixels give finer detail and give you more freedom to crop.