See the picture to the left? You can easily make this in 3 simple steps. Scanlines seem to be in style today, and it's good to learn a few things, even if you don't think you'll need them, it'll give everything more detail, and it will look cool!

You need to download this file to make your scan lines [ link ]

Open up your image, select the layer you want to be scan lined, and click Filter, Texture, then Texturizer... and your window should look this the one to the left, click 'Load texture...' and load the texture that you downloaded, you may want to mess with you scan lines I used this info:
Scaling: 62%
Relief: 3%
Light Direction: Top (default)