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JPEG, short for Joint Photographic Experts Group, is a widely used method of lossy compression for digital images. It was developed by the Joint Photographic Experts Group and published in 1992 as part of ISO/IEC 10918 and ITU-T T.81. The format is commonly used with the file extensions .jpg or .jpeg and is often accompanied by metadata standards such as Exif and JFIF.

The JPEG compression process transforms image data from the spatial domain to the frequency domain using an 8x8 block-based discrete cosine transform (DCT). The resulting coefficients are quantized, discarding detail in a controlled way, and the remaining data are entropy coded with Huffman coding (with some variants using arithmetic coding). Images are typically encoded in the YCbCr color space with chroma subsampling (for example 4:2:0), reducing resolution for color information to save space. Most JPEG files use 8-bit samples, though higher bit depths are possible in some professional applications.

Baseline JPEG provides fast decoding and broad compatibility; progressive JPEG allows the image to be progressively refined as data arrives, improving perceived loading times on the web. JPEG images are often accompanied by camera metadata in Exif format, including exposure settings, timestamps, and GPS data.

Applications and limitations: JPEG is the de facto standard for photographs and web images because of its balance between quality and file size and its broad support across devices and software. Limitations include visible artifacts at high compression, especially around sharp edges, and the lossy nature that prevents exact reconstruction of the original image. Related standards include JPEG 2000, a different compression approach that is not as widely adopted.