Method for forming a reconstruction image ( I k), the reconstruction image showing a position ( x, y) of irradiating sources (10 a, 10 b) in an observation field (Ω), the method employing a device comprising a gamma camera joined to a visible camera, the device being such that: - the gamma camera and the visible camera define the observation field (Ω); - the visible camera is configured to form a visible image ( V k) of the observation field (Ω); - the gamma camera comprises pixels, which are configured to detect ionizing electromagnetic radiation generated by an irradiating source potentially present in the observation field, the pixels lying in a detection plane; - the gamma camera is configured to form a gamma image ( M k), allowing a position, in the field of observation, of irradiating sources, the radiation of which is detected by the pixels, to be estimated; the method being characterized in that it comprises the following iterative steps: a) at an initial measurement time (k=1), acquiring an initial gamma image ( M 1) with the gamma camera and acquiring an initial visible image ( V 1) with the visible camera; b) on the basis of the initial gamma image and of the initial visible image, initializing the reconstruction image ( I 1); c) acquiring a gamma image ( M k) with the gamma camera and acquiring a visible image ( V k) with the visible camera, at a measurement time ( k); d) comparing the visible image ( V k) at the measurement time with a visible image ( V k -1) at a prior time ( k -1), the prior time being the initial measurement time or a preceding measurement time, then, depending on the comparison, estimating a field ( D k) of movement between the visible images acquired at the prior time and the measurement time, respectively; e) updating the reconstruction image ( I k), depending: - on a reconstruction image ( I k -1) established at the prior time; - on the movement field ( D k) resulting from step d); - and on the gamma image ( M k) acquired at the measurement time; f) optionally superposing the reconstruction image, or a portion of the reconstruction image, and the visible image; g) reiterating steps c) to f) while incrementing the measurement time, until the iterations are stopped; the device being moved between at least two measurement times, such that one observation field (Ω k) corresponds to each measurement time ( k). - the gamma camera and the visible camera define the observation field (Ω); - the visible camera is configured to form a visible image ( V k) of the observation field (Ω); - the gamma camera comprises pixels, which are configured to detect ionizing electromagnetic radiation generated by an irradiating source potentially present in the observation field, the pixels lying in a detection plane; - the gamma camera is configured to form a gamma image ( M k), allowing a position, in the field of observation, of irradiating sources, the radiation of which is detected by the pixels, to be estimated; a) at an initial measurement time (k=1), acquiring an initial gamma image ( M 1) with the gamma camera and acquiring an initial visible image ( V 1) with the visible camera; b) on the basis of the initial gamma image and of the initial visible image, initializing the reconstruction image ( I 1); c) acquiring a gamma image ( M k) with the gamma camera and acquiring a visible image ( V k) with the visible camera, at a measurement time ( k); d) comparing the visible image ( V k) at the measurement time with a visible image ( V k -1) at a prior time ( k -1), the prior time being the initial measurement time or a preceding measurement time, then, depending on the comparison, estimating a field ( D k) of movement between the visible images acquired at the prior time and the measurement time, respectively; e) updating the reconstruction image ( I k), depending: - on a reconstruction image ( I k -1) established at the prior time; - on the movement field ( D k) resulting from step d); - and on the gamma image ( M k) acquired at the measurement time; - on a reconstruction image ( I k -1) established at the prior time; - on the movement field ( D k) resulting from step d); - and on the gamma image ( M k) acquired at the measurement time; f) optionally superposing the reconstruction image, or a portion of the reconstruction image, and the visible image; g) reiterating steps c) to f) while incrementing the measurement time, until the iterations are stopped;