artifacts in processed images

Question

This question is related to my previous post Image Processing Algorithm in Matlab in stackoverflow, which I already got the results that I wanted to.

But now I am facing another problem, and getting some artefacts in the process images. In my original images (stack of 600 images) I can't see any artefacts, please see the original image from finger nail:

But in my 10 processed results I can see these lines:

I really don't know where they come from?

Also if they belong to the camera's sensor why can't I see them in my original images? Any idea?

Edit:

I have added the following code suggested by @Jonas. It reduces the artefact, but does not completely remove them.

%averaging of images
im = D{1}(:,:);
for i = 2:100
 im = imadd(im,D{i}(:,:));
end
im = im/100;
imshow(im,[]);

for i=1:100
SD{i}(:,:)=imsubtract(D{i}(:,:),im(:,:))
end

@belisarius has asked for more images, so I am going to upload 4 images from my finger with speckle pattern and 4 images from black background size( 1280x1024 ):

And here is the black background:

Answer 1

Your artifacts are in fact present in your original image, although not visible. Code in Mathematica:

i = Import@"http://i.stack.imgur.com/5hM3u.png"

EntropyFilter[i, 1]

The lines are faint, but you can see them by binarization with a very low level threshold:

Binarize[i, .001] 

As for what is causing them, I can only speculate. I would start tracing from the camera output itself. Also, you may post two or three images "as they come straight from the camera" to allow us some experimenting.