Camera Shake
Image blur caused by camera movement during exposure, resulting in the entire image appearing smeared in one direction.
Camera shake occurs when the camera body moves while the shutter is open, causing the entire image to appear blurred in a directional streak. It is most common in low-light situations with slow shutter speeds (below 1/60 second) or when using telephoto lenses.
The general rule to avoid shake is to use a shutter speed of at least 1/focal-length seconds. For example, a 200mm lens requires at least 1/200 second. Physical countermeasures include using a tripod, bracing against a wall, and keeping elbows tucked in while shooting.
Modern cameras and smartphones feature Optical Image Stabilization (OIS) or In-Body Image Stabilization (IBIS), compensating for 2 to 5 stops of shake. Post-capture correction through sharpness processing can partially improve mild shake, but severe blur is nearly impossible to fully restore. Unlike focus blur, camera shake produces a characteristic directional smear across the entire image.