import cv2
import numpy as np

img = cv2.imread('captcha1.jpg')
phase = -0.8 * np.pi
omega = 2.0 * np.pi / img.shape[1]
amp = 15.0

x = np.arange(img.shape[1], dtype=np.float32)
y = np.arange(img.shape[0], dtype=np.float32)
xx, yy = np.meshgrid(x, y)
u = 0.0
v = np.sin(phase + xx * omega) * amp

corr = cv2.remap(img,  xx + u, yy + v, cv2.INTER_LINEAR)
cv2.imshow('in', img)
cv2.imshow('out', corr)
cv2.waitKey()