This tutorial is very similar to the grid tutorial. You want an image with scanlines, but you don't want scanlines over the entire image right? Just follow this tutorial ^^

1 Just for this tutorial, use this image of mine.
2 Select all of the image, copy it, and then open a new image. [The size will be on there already] and then paste it!
3 Create a new layer. 4 Now, minimize that, and create a new image. The new image will be your scanline pattern. Make a new document. My new image is 1x2. 5 Take the pencil tool, and make it 1px. Select a color of your choice [I'm doing white] and draw one dot in the new document.

[I have magnified mine by 1600% and ignore the border. I put it there so you can see it better!]
6 Okay, keep it open and go to Edit, Define Pattern. Name the pattern grid or something.
7 Now, back to the image you want the scanlines on.
8 Once you have that open, select the pattern stamp tool.

[Click on the stamp and hold down, until you get to the pattern stamp tool!]
9 Okay, a menu thingie should pop up on the top. Where it says PATTERN, click the down button and find your grid pattern ^^
10 Choose a brush size and opacity and color all over your image where you want the grids to be =) Keep changing the opacity to make it different in areas.
11 If you mess up, just use the eraser tool ^^ Now you can do pretty scanlines!! =D