In this paper we describe a citizen-science project designed by the Spanish Virtual Observatory (SVO) to precover NEAs in the Eight Data Release of the Sloan Digital Sky Survey. Discovery alone is indeed not enough to quantify the threat level of a near-Earth asteroid (NEA). Above all, it is necessary to compute reliable orbits through accurate astrometric positions covering a period of time as long as possible. Precovery (short for "pre-discovery recovery") is the term that describes the process of identifying an object in archive data whose presence was not detected at the time the observation was made.