Why Do Megapixels Matter?
The amount of megapixels a photograph has indicates how detailed the photo is. Generally, the higher the megapixel number, the better the detail. On digital prints, low megapixel count is noticeable, as lines are ill defined, colors are blurred, and any solid colors have a lot of "noise". With higher megapixel count, images are crisper, and closer represent the way the moment looked in reality.
Digital or Prints
If you're a social networking addict who uploads photos to the Internet with little desire to own a physical copy, 5 megapixels is more than enough. If you love making prints, especially large prints (8x10 or more), plan on investing in at least 5 megapixels. If you're seeking to make larger prints, such as 16 x 20, you'll need around 18.4 megapixels to attain optimum quality.
Decoration or Leisure
What are your plans for the photographs you're taking? If you're hoping to make a mural in your home of high-quality photos of varying sizes, invest in a camera with around 8-10 megapixels. If you just need a camera for everyday use and may get the occasional 4x6 print (the standard photo print size), you will be fine with 5 megapixels.
Point and Shoot Cameras
Point and shoot cameras are the everyman's camera: just point and shoot with little regard for the camera's settings. Quality P&S cameras come with 12.1 megapixels, but you can get away with far less than that: 5-7 megapixels is recommended for average camera use.
If you're seeking to be more than an amateur photographer, consider getting an SLR camera (camera with removable lens). With an SLR, you have more control over shutter speeds, ISO, white balance, and focus. Quality SLR cameras begin at around 6.1 megapixels and can be bought for around $400 used, but for a mere $50-$100 more you can easily find an SLR camera with 10.2 megapixels.
Pixel Size Matters
Pixels are "minute areas of illumination, one of many from which an image is composed".
The average person likely doesn't know anything about pixels, but knowing the pixel size of the camera you're about to purchase can make a large difference in quality. In cameras with low pixel sizes, "noise" is visible: the pixels show up as thousands of dots across the picture.
The larger the pixel, the more photons (amount of light) each pixel collects: similar to collecting more raindrops with a larger bucket. High-end cameras use larger pixels with high megapixel count and create crisp, seamless images. Consumer cameras boast 15.1 megapixel counts, but with very small pixels-which results in a lot of image noise. Therefore, it is better to have a camera with 5 or 7 megapixels with large pixels than 12.1 or 15.1 megapixels with small pixels.
The average consumer will be content with 5-7 megapixels, but if your goal is to take beautiful, crisp images with a lot of detail and minimal noise, consider pixel size before making your final purchasing decision.