Click the Create a New Layer button () in the Layers palette. (It doesn’t matter which layer is currently selected because you’re going to move the new layer a little later.)

Double-click the new Layer 1, and type Image Border to rename it.

Drag the Image Border layer to the top of the Layers palette stack, until a black line appears immediately above the Words layer set, and then release the mouse button.

The Image Border layer is now the top layer in the image.

Choose Select > All to select the entire image.

Choose Edit > Stroke. In the Stroke area, enter 5 px for Width and click OK. (Or, for a more dramatic black border, enter a larger number, such as 10 or 15 pixels.) A 5-pixel-wide black stroke now appears around the entire image.

Choose Select > Deselect to deselect the entire image.

Choose File > Save.