[ctaulbee]

Four ways were posted in another thread here, they are in one post, pick whichever works best for you

Arccuk - Ctrl+A to select all, then add a 1 or 2 pixel stroke.

JupiterPrime - CTRL-P or Print with preview, press teh BORDER button, add a 1 mm border.

Ctaulbee - Set your background to black change the canvas size (Photoshop under Image\Canvas Size) by adding 4 pixels to the width and height both this will give you a 2 pixel border around the outside then print.

RickT - Set photoshop to add corner crop marks