1. Open Photoshop. Open an image to apply line effect.
2. Desaturate the image by Image > Adjustments > Desaturate
3. Create New file with 1 pixel width, 2 pixel height and transparent background.
4. Keep Black as a foreground color. Fill the top 1 X 1 pixel of transparent background using Pencil Tool.
5. Select All using CTRL + A
6. Create a pattern by Edit > Define Pattern. Name the pattern.
7. Close the Pattern file and go back to image file.
8. Edit > Fill
(Choose “Pattern” from “Use” drop down menu and again in “Custom Pattern” you will find newly created pattern)
9. Select newly created pattern and fill the image.
Source : http://www.tutorialguide.net/line_effect_tutorial.html