Occluding squares.

(sqr1): The original image.
(sqr1can1): Result of applying the Canny edge detector to sqr1.
(sqr1can2): Result of adding 1% salt and pepper noise to sqr1can1.
(sqr1can3): Result of image editing sqr1can1.
(sqr1hou1): Hough transform of sqr1can1.
(sqr1hou2): Histogram equalized version of sqr1hou1.
(sqr1hou3): Lines found from analysis of Hough transform of sqr1can1, overlaid on top of original image sqr1.
(sqr1hou4): Hough transform of sqr1can2 (after histogram equalization).
(sqr1hou5): Lines found from analysis of Hough transform of sqr1can2, overlaid on top of original image sqr1.
(sqr1hou6): Hough transform of sqr1can3 (after histogram equalization).
(sqr1hou7): Lines found from analysis of Hough transform of sqr1can3, overlaid on top of original image sqr1.