I've seen some popular Youtube thumbnails pictures using this technique to put a colored border. It makes the thumbnails standout among the rest.
The steps to do it in Adobe Photoshop is quite simple.
Basically just fire up Photoshop, and it requires only 2 steps :
Go to Image -> Canvas Size. Make sure the Relative checkbox is set. then put in the size of the border. For my case I use 0.5 inches, if you want to have thicker border then set the value higher.
There's a color selection at the bottom dialog box to set the color of the border.
