In this paper we present the usefulness of the algorithm DCT (Discrete cosine Transform) blocks applied level image compression JPEG (Joint Photographic Experts Goup). It has been shown that this algorithm is the most efficient in the case of compression because it has very good properties for compaction energy related values. As a basic principle we eliminate high frequencies and keep the low and medium without visibly affecting image. DCT in JPEG compression algorithm is encountered in practical applications such as face detection, skin color, facial recognition, iris, fingerprints