This is an ultra-easy tutorial that can add a powerful effect to images.

Step 1

Start with an image. Mine is from a friend over at deviantart.

Step 2
->
Create a new layer. On that layer, select the gradient tool and make a small straight line, like above.

Step 3

On your gradient layer, lower the opacity like above (70% worked good for me, you can experiment if you wish)

Final Product

Mine looked like this. Its a pretty simple tutorial, so if you have any questions or comments, please post below!