Problem solved Allan
At "start new picture" you should choose the "transparent" option!
(the options are : white, background color and transparent)
Now make your 20 stripes as I wrote before.
Go to select tool : "Ellipse" and make a circle in the middle of a stripe. Hit the "Del" button. Move your circle to the next one and hit Del again etc...
Now you can save your greyscale as a PSD file. (not JPG, very important!)
Load your BW picture and add your greyscale as a new layer. You can move it, scale it, etc.. but you will see always through the holes.
See photo:
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