1. A rolled fingerprint acquisition method which automatically detects a start and end of registration and synthesis, comprising: extracting fingerprint characteristic information of fingerprints included in rolled fingerprint frames that are sequentially acquired; comparing at least one of the fingerprint characteristic information and the amount of variation between the fingerprint characteristic information to reference fingerprint characteristic information to determine whether to start or end registration and synthesis; and registering and synthesizing the rolled fingerprint frames according to the result of the determination, wherein the registering and synthesizing of the rolled fingerprint frames comprises: setting a first reference line for dividing a region where a first foreground corresponding to a fingerprint of a first rolled fingerprint frame that is a rolled fingerprint frame acquired after it is determined that registration and synthesis should be started overlaps a foreground corresponding to a fingerprint of a second rolled fingerprint frame; setting at least two of points that are included in the second foreground and are on the reference line as control points; calculating displacements from the control points to points that are on the first rolled fingerprint frame and match the control points; registering the second rolled fingerprint frame with the first led fingerprint frame based on the displacements to create a first registered frame; moving the control points by the displacements and connecting the moved control points to set a second reference line; and synthesizing the first registered frame with the first rolled fingerprint frame using the second reference line.