1. Biometric device for capturing fingerprint information and for extracting significant data from a partial fingerprint area, comprising processing means, a line sensor for consecutively capturing fractional fingerprint images from fractional areas of a finger through a relative sliding movement between the finger and the line sensor, means for consecutively storing the fingerprint information in a first memory, decision-making means for deciding when the information stored in the first memory constitutes a partial fingerprint area, extraction means for extracting significant data from the partial fingerprint area stored in the first memory and for storing the extracted significant data in a second memory, wherein the captured fractional fingerprint images are stored in the first memory in such a way that several consecutive fractional fingerprint images are compared with the previously captured fractional fingerprint images, and are combined together to form a partial fingerprint area which is large enough for the extraction of the significant data, and where the oldest stored fractional fingerprint image is discarded from the first memory when new fingerprint image is stored in the first memory.