Step 1 : I have opened this free stock photo in Photoshop.

Step 2 : Make sure that the Foreground Color is set to the default Black and Background to White.

Step 3 : Go to Edit>Canvas Size

Step 4 : The Canvas Size dialogue box opens. Check Relative. The Width and Height are now set to 0 cm. Type in 1 cm for both Width and Height. There is nothing hard and fast about this of course. Click ok.

You can see a White Frame around the image.

Step 5 : Now change the Foreground Color to White and Background to Black by clicking on the small bent arrow.

Step 6 : Again go to Image>Canvas Size.

Step 7 : You will find that Relative is checked. Type in 3 cm for both Width and Height. Again nothing hard and fast about it. Click ok.

And there is your Black and White Frame. How long did it take? It's extremely easy.