If this does not make you lose too much information, one approach could be to apply a horizontal motion blur filter to the image, then binarize it, like so:
I = imread('compImg.jpg');
h = fspecial('motion', 300, 0); % Apply motion blur
I = imfilter(I, h);
imshow(I);
BW = imbinarize(I, 0.60); % Apply threshold
mask = true(size(BW));
mask(:, 200:end-200) = false;
BW(mask) = 1;
imshow(BW)
This would need some tweaking, but once you can successfully isolate the resin interlayers, you can use a method such as the Hough Transform to detect these lines.
