Step 1
Start out by finding an image you would like to add this trendy attribute to. below is the image i wil be using for this tutorial.
Step 2
Now using the rectangular marquee (press m) select an area 1px wide and as high as you would like the strech to be. seeing how the image i choose is small i have selected 1px as high and low as i could. with your selection press ctrl+t (to transform, or right click and go to free transform). drag your selection as far right or left as you like then hit enter and apply your change! below is my result.
Tips:
with this tutorial you you can make simple borders for your site. i do this all the time to make mine.
More Tutorials: 
