Probability distribution (filled bars) and cumulative function (blue line) of the length, expressed in pixels of 0.186 arcsec in size, and the length-to-width ratio of all objects detected with the arcfinder before the application of the final geometrical and colour selection, in the left and right panels, respectively. The vertical green lines represent the respective lower limits adopted for the final candidate selection to maximize the completeness given the limits imposed by the data PSF.