bg = imread("ngc6543a.jpg");  
figure;
imshow(bg);
hold on;
x = linspace(1, size(bg,2), 100);
y = sin(2*pi*x/size(bg,2)) * size(bg,1)/3 + size(bg,1)/2;
h = plot(x, y, 'r-', 'LineWidth', 4, 'Color', [1 0 0]);