Blurry images are the cause of camera shakes. While shooting with lower shutter speed the images often get blurry even if there is a slight shake of the camera. To take sharp images and avoid blur, take support of what ever help that is available i.e use a tripod, lean against a wall, lie down on your elbows, use anything that is available. Also use faster ISO.
Sometimes there are unwanted color lines around the dark subject in the image. This phenomenon is called chromatic aberration. It is causer due to the failure of a lens to focus all colors to the same point. To minimize chromatic aberration use larger aperture, for example try f4,f3.5,f2.8 and use software to correct the chromatic aberration.
Depth Of Field :
Many images have a very good subject and composition but they loose the race of being a really appreciable image due to inappropriate depth of field. The depth of field (DOF) is the portion of a scene that appears sharp in the image. Good images have proper depth of field. Depth of field can be controlled by the aperture settings. e.g Use larger aperture value while shooting portraits and smaller aperture value while shooting landscapes. Proper depth of field is a must for best images.
Lens flare is created when non-image forming light enters the lens and hits the camera sensor. It normally appears as polygonal light orbs and it is very common while shooting in sun. Lens flare not only creates unwanted orbs in the image but also decrease the contrast of the image. The best way to reduce and almost eliminate the lens flare is to use a camera hood.
Image noise is a random, usually unwanted, variation in brightness or color information in an image. Some level of noise is required in the image but the higher levels can give undesirable results. Image Noise is directly proportional to ISO speed an inversely proportional to light. Low light high ISO speed means more noise in the image. Use software like NeatImage to reduce noise in the image.
Overexposure occurs when excess light falls on the sensor/film than required. An overexposed image has white parts effectively all white i.e. loss of highlight details. Usage of proper shutter speed and metering can avoid overexposure and produce a well exposed image. Also to some level exposure can be corrected using software.
Red-eye is the most common problem faced by the photographers using a flash. Red-eye is the outcome of the reflection of light from the open retina of the eye. Nowadays most of the digital cameras come with an option of red-eye reduction. Don't hesitate to use this option while shooting humans and animals using a flash. Otherwise use software to correct the red eye.
This is a very common defect while shooting landscapes involving horizons(hence the name tilted horizons) or verticle objects like buildings. In this, the image is not leveled, it is tilted at some small angle which might not be noticeable at the time the shot is taken. It appears when the image is seen on a larger screen, like the computer screen. To avoid tilted horizons always use a tripod and level it with the ground level.
Underexposure occurs when less light falls on the sensor/film than required. An underexposed image has dark parts indistinguishable from black i.e loss of shadow details. Again Usage of proper shutter speed and metering can avoid overexposure and produce a well exposed image. Also to some level exposure can be corrected using software.
vignetting is the phenomenon in which the corners of the image are more darker than the center of the image. The pixels of the sensor which are at the right angle to the light are well lit and bright and the other pixels receive less light hence darker impression.Most digital cameras use built-in image processing software to compensate vignetting when converting RAW sensor data to standard image formats such as JPEG or TIFF. Otherwise use software to correct vignetting.