An easy and effective way to create a "Polaroid" type border for your photographs (though follow the steps in order!) Open your image in rgb mode. Increase canvas size by 40 pixels for height and width. Now, duplicate the layer.

Fill the duplicate layer with white. Make a selection for your border on the duplicate layer. Now, move the duplicate layer underneath the original.

Deselect. Access layer styles from the Pallet Menu with drop shadow at the default settings and Outer Glow with the blending mode set to Screen, 50% opacity. Flatten the image from the Layers Palette and you're done!