1. A method of constructing an image of a petroleum reservoir, from dynamic data measured within the reservoir, comprising the steps of: a) generating with a computer at least two independent realizations of the reservoir from at least two Gaussian white noises; b) defining at least one region within the at least two independent realizations and defining a parameter allowing size and shape of the at least one region to be modified; c) generating a new realization of the reservoir from a linear combination of the Gaussian white noises with linear combination coefficients dependent on the parameter allowing the at least one region to be modified; d) calculating a local objective function measuring, within the at least one region, a difference between dynamic data simulated from the new realization and the measured dynamic data; and e) constructing the image of the reservoir with a computer by modifying the parameter for minimizing the local objective function and the generation of the new realization of the reservoir in accordance with step c).