Life recognition is desired for unattended fingerprint identification. We look at the color changes in a series of fingerprint images acquired during the course of an input action. As we press a finger upon an input device, a fingerprint area gradually increases and its color changes. This is due to the blood movements induced by a finger deformation. For example, we can declare a finger is alive if its color change exceeds a certain value. However, the color changes in the images acquired by a conventional device using a prism are very small. This is because the light reflected by the valley regions of a finger carries little information about the blood movements. We tried a fingerprint sensor based on scattered light detection. Here, a plastic plate serves as a light-guide for LEDs mounted on its edge. When a finger is pressed against the plate, the propagating light is scattered by the finger and leaks out of the plate. A standard color CCD camera placed near the plate captures the scattered light. Data extracted from more than ten people of different age groups indicate that there is a certain minimum value for the color changes.