artifact

A distortion in an image or sound caused by a limitation or malfunction in the hardware or software. Artifacts may or may not be easily detectable. Under intense inspection, one might find artifacts all the time, but a few pixels out of balance or a few milliseconds of abnormal sound often go undetected.

Analog Artifacts
In films and film-based videotape, artifacts such as blotches, scratches and flicker are commonly found, especially in older movies. Imperfections in the camera lenses and CCDs, and the silver-grain film itself, can generate "noise," which appears as tiny background specks, making the image softer. The electronic recording of analog videotapes can introduce noise as well. See noise.

Digital Artifacts
Artifacts are a natural byproduct of digital compression methods such as JPEG and MPEG, which permanently discard pixels. The greater the compression used, the more artifacts are likely, and fast motion sequences are a major contributor. As TV screens become larger, the distortions are more noticeable. In digital cameras, artifacts may arise when performing digital zoom. When analog material is converted to digital, tiny discrepancies (quantization errors) may result. See blocking artifacts, mosquito noise, feathering and quantization error.