Right. To get to the chase, patterns is an amazingly nice thing if you wish to:

- Copyright an image
- Add Great Scanlines
- And More!

They're very easy. Start by making a pattern. Make a new document, 1x2. Select the Pencil Tool and do this:



Makes no sense, right (Unless you've worked with patterns before)? Now go Edit -> Define Pattern....
Type something in the text field and click OK.
Now open your image, I started with this:



Was easy stuff, no big deal or anything but hell...
Anyways, make a new layer (CTRL+SHIFT+N) and go Edit -> Fill...

Use these settings (Adjust Opacity if you wish):



Click OK

My image looked like this after adding the effect:



Some other ones are the following (Pattern is in the little field, use same progress):







Quick written, because I have to close. Good luck on it!