1.
Make a new image and choose transparent background. Next make a 1x3 selection and fill it with black or the color of your choice. Or you could download my .psd file for this by clicking the icon



 

2.
Next grab the edit/transform/rotate tool and turn the image like I have it in the picture. ( If you downloaded my file, zoom in to 1600% )

3.
Next make a 3x4 selection and set the marque like I have mine. Then go to edit/define pattern.

4.
Now select the part of your image that you want to use this in. Then go to edit/fill and then make sure you select pattern.

5.
This turns out pretty cool and it's not the same old boring scanline. So try it out as an alternative to the old traditional scanlines :)

Tutorial Source