The invention provides a linear sensor including a row 100 of N regularly spaced pixels that are formed in a semiconductor substrate, and a circuit for reading out the N pixels, which delivers an output signal for each of the N pixels of the row, characterized in that the N pixels comprise image-capturing pixels that have a useful photosensitive area in the shape of a rectangle R that is higher than it is wide, where the width is in the direction of the row and the height is in the perpendicular direction, and at least two spaced-apart pairs of alignment-detecting pixels PPL, PPR, wherein the detecting pixels of each pair are pixels P1, P2 that are adjacent in the row 100 of pixels and the useful photosensitive area DT1, DT2 of the detecting pixels has a width that varies monotonically in the height direction, but in opposite directions for the two detecting pixels of a given pair.