Create a new layer, 1 pixel wide, 2 pixels high, and with a transparent background, then zoom in to 1600% (the furthest).
Take your pencil tool and press D to reset your colours, then fill in the top pixel as shown below.
Now click Edit>Define Pattern... Then choose a name for your pattern, i've called it Scan Lines.
You can now close this file without saving it.
Take a picture you wish to add the lines to, i'll be using this one shown below, feel free to save it and use it for yourself.
Now on the same layer as your picture, select your styling list and choose pattern overlay.
Now select the drop down box and choose the pattern.
Change the setting of the opacity to around 50% for this image, but other images require deeper colouring, just play around till you get your desired effect.
And here we go...
