Results of MC simulations in the GOODS-North and -South fields using the prior source extraction method. These MC simulations correspond to the central deepest regions of each field, i.e., avoiding the rather noisy edges of the GOODS-N field and concentrating on the GOODS-S-ultradeep part of the GOODS-S field. Blue lines represent the average photometric accuracy defined as the standard deviation of the (S_out − S_in)/S_out distribution in each flux bin (after 3σ clipping). Red lines show the mean value of the (S_out − S_in)/S_out distribution in each flux bin. Inset plots show the fraction of artificial sources detected in the image (i.e., completeness) as a function of input flux (orange plain histogram) and the fraction of spurious sources (i.e., contamination) as a function of flux density (striped black histogram).