Pequeno script que cria um captcha visual, gerando números aleatoriamente. Tira partido do módulo PIL (Python Image Library) e do módulo random.

Módulo PIL - Python image library

Nota: O threshold varia a intensidade dos pontos brancos.

import Image, ImageDraw, ImageFont, random
 
#settings
number = str(2)
random.seed()
number2 = str(random.randint(0,100))
limit = 50
threshold = 50
 
#constants
size = 360, 220
black = 0, 0, 0
white = 255, 255, 255
tmp = 0, 0
 
#random position
x = random.randint(0, size[[0]]-110)
y = random.randint(0, size[[1]]-100)
 
#create objects
im = Image.new('RGB', size, black)
font = ImageFont.truetype("folks-bold.ttf", 13)
font2 = ImageFont.truetype("verdanab.ttf", random.randint(95,100))
font3 = ImageFont.truetype("ariblk.ttf", random.randint(95,100))
font4 = ImageFont.truetype("verabd.ttf", random.randint(95,100))
draw = ImageDraw.Draw(im)
 
#random black dots in the background
for i in xrange(size[[0]]):
    for e in xrange(size[[1]]):
        if random.randint(0,threshold) == 0:
            draw.point((i,e), white)
 
#write the text
fontmask = font.getmask(number, mode="")
fontmask.rotate(10)
draw.text((size[[0]]-15, size[[1]]-20), number, font=font)  
 
for i in number2:
    rnd = random.randint(2,4)
    if rnd == 2:
        draw.text((x+tmp[[0]], y), i, font=font2)
        tmp = font2.getsize(i)
    elif rnd == 3:
        draw.text((x+tmp[[0]], y), i, font=font3)
        tmp = font3.getsize(i)
    else:
        draw.text((x+tmp[[0]], y), i, font=font4)
        tmp = font4.getsize(i)
im.show()

*Discussão no fórum