1. A method for determining confidence values for voxels, the method comprising: a) acquiring real projections of an object in a tomography system, wherein each real projection includes a plurality of pixel values, each pixel value corresponding to a respective penetrating-wave beam; and reconstructing an image of the object from the real projections, the image including a plurality of the voxels; b) generating a confidence value for each of the voxels by: computing a manifold of error measures for different penetrating-wave beams through the voxel, wherein each of the manifold of error measures is computed for one of the pixel values as a difference between the one of the pixel values and a summation of a product of a weighting factor and respective voxel values for voxels through which the respective penetrating-wave beam passes; building a histogram from the manifold of error measures; converting the histogram to a probability distribution; and deriving a characteristic value from this probability distribution.