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Noise in digital images
Randomly-spaced speckles, known as noise, can appear in digital images. Noise is caused most often when taking photos with a digital camera using a high ISO number, usually over ISO 100. When noise is present in a photo, detail and clarity are reduced. 
Noise is most noticeable in even areas of color such as shadows and in a sky. The good news is that there are steps you can take to minimize, if not, prevent noise. In addition, there are special software programs that do an effective job at noise reduction.
Noise is primarily seen when viewing a photo on a computer monitor at 100%. But when an image is reduced in size, noise is rarely visible. Noise is not noticeable in small sized prints. The exception is when a very high ISO setting is used (see below).
Preventing noise
Unlike digital single reflex cameras that have large sensors, most compact digital cameras have limited light sensitivity.
When possible, keep the ISO setting at 100 or below to help prevent noise. If a shutter speed is under 1/60th of a second and your camera doesn't have image stabilization, steady the camera using a tripod or other support when shooting.
Shooting in low light
Using a flash can help prevent image noise if you stay within the recommended flash range. If you prefer not to use the flash, increase room lighting. Let outside light into the room through doors and windows. Turn on more room lights but also select an appropriate white balance setting.
In-camera noise reduction
Some digital cameras include a Noise Reduction setting. When turned on, noise reduction takes place whenever shots are taken at very slow shutter speeds. While noise reduction works, in some cases image detail may be smeared.
Shooting at very high ISO numbers
Some consumer digital cameras have a high sensitivity mode, or the capability of shooting at ISO 800, 1600 and higher. The quality of images produced using high ISO can be significantly degraded unless you have a camera capable of handling it well. Test your camera to see the highest number you can tolerate.