Here is the final result of scanline effect created by photoshop.
It's a amazing effect which is used everywhere on internet nowadays. It's cool to apply this to your website or your signature. The coolest thing is that it's very easy to create by photoshop
So let's start.
1. create a transparent file 1x3 and putt a black dot in the middle.
2. Click Edit>Define Pattern and save your pattern.
3. Open the image you want to apply the effect.
4. Click Edit>Fill and choose "pattern" which you just created.
5. Not good? ok, adjust the opacity to 70%, 50%, and 30%.... Which one you like? The following is 30%
So simple? Yes. Photoshop always makes thing simple.