You'd be surprised at how adding a frame can really make a difference to an image and they're really simple to create in Photoshop.
First, you need to open your image and once you've done this, in the layers window, double click on the background layer to change it into a basic layer and rename it.
Next, go to image>increase canvas size and this will open a new window where you can alter the width and height of the canvas. If you tick the relative box and put 100 pixels into width and height, 50 pixels of canvas space will be added to each side of the image. Once you're happy click OK.
From here, we want to create a new layer to add a band of colour to the frame. You can do this in the layers window or by going to layer>new layer. Select the new layer and use the fill tool to colour the layer (we used white).
Click back on your image layer holding down the CTRL key (on a PC) to select it with 'running ants', then create another new layer where we'll create the frame in. To do this, go to edit>stroke and a new window will open. In here, you can pick the colour of the line, the width and the location of it. Once you click OK you'll see the border appear around the image. If you're happy, deselect the image (select>deselect).
If you want to, you can also add a drop shadow to the frame. You do this by clicking on the fx icon found at the bottom of the layers window. Once you find the drop shadow option and click on it, a layer style window will open. In here you can adjust several things including the opacity and angle of the drop shadow. Once you're happy with how the drop shadow looks, click ok and take a look at your finished image.
Here's the image with a frame: