If the noise is exactly horizontal, one straight-forward solution would be like this:
% Read your image and convert it to gray-scale
I = imread('img.jpeg');
Igray = rgb2gray(I);
% Extract the target region
Igray = imcrop(Igray,[178 20 443 443]);
% Estimate line noise in horizontal direction
rowAvg = mean(double(Igray),2);
rowNoise = rowAvg - mean(rowAvg);
% Cancellation of noise
Igray2 = double(Igray) - rowNoise;
Igray2 = uint8(Igray2);
% Compare original and processed image
figure
subplot(1,2,1)
imshow(Igray)
title('Original image','FontSize',16)
subplot(1,2,2)
imshow(Igray2)
title('After processing','FontSize',16)
