from PIL import Image, ImageOps
from ImageFilter import *
WHITE = 255
BLACK = 0
MARGIN = 2
img = Image.open('capt.png').convert("RGB")
# remove filled squares
img = img.filter(MinFilter(3)).filter(CONTOUR)
# to monochrome
img = img.convert('1')

pixels = img.load()
vert_lines = set()
horiz_lines = set()
# get vertical lines
for x in xrange(img.size[0]):
    if pixels[x, MARGIN] == BLACK:
        vert_lines.add(x)
# get horizontal lines
for y in xrange(img.size[1]):
    if pixels[MARGIN, y] == BLACK:
        horiz_lines.add(y)
# remove lines
for x_coord in vert_lines:
    for y in xrange(img.size[1]):
        pixels[x_coord, y] = WHITE
for y_coord in horiz_lines:
    for x in xrange(img.size[0]):
        pixels[x, y_coord] = WHITE
# cut off the border
img = ImageOps.crop(img, border = MARGIN)

img = img.filter(MinFilter(9))

>tesseract img1.bmp con digits
Tesseract Open Source OCR Engine v3.01 with Leptonica
2560

img = Image.open('capt2.png').convert("RGB")
# remove filled squares
img = ImageOps.grayscale(img)
pixels = img.load()
for y in xrange(img.size[1]):
    for x in xrange(img.size[0]):
        if pixels[x,y] > WHITE / 2:
            pixels[x,y] = WHITE
        else:
            pixels[x,y] = BLACK

img = img.filter(MinFilter(3)).filter(CONTOUR)