random change of color pixel with PIL

[mlieqo]

(r, g, b) = picture_1.getpixel((x,y)

You don't need color of pixel from your original picture because you dont actually use them

So altogether, with loop changed to this:

for x in range(largeur) :
    for y in range(longueur) :
        r = randint(0,25)
        g = randint(0,255)
        b = randint(0,255)
        picture_2.putpixel((x,y), (r, g, b))

it will create a new image with the same size as your original picture and every pixel will have random color.

Or is this not actually what you wanted? :D