How to add this shadow effect in photoshop

Here is what I'm trying to do on the border of a photo.

How can I do this in photoshop?

Thanks,

Answer

It's a drop shadow. You can use layer fx for that. Select the layer, go to the bottom of the panel where there is a little 'fx' menu and choose 'drop shadow'. Set the distance to 0 if you want it the same on all sides.