Adding a Stroke to a Photo
Open the photo you want to add a stroke to. I am using the photo below:

Select Edit > Stroke Selection:
This will open the stroke option dialog box shown below. This is where you can choose your color, size of your stroke, how you want the stroke to appear around the image, and the blend mode for the stroke. I selected a color from my photo by clicking on the red color swatch by the work Color, then put my eyedropper
over the photo until I found the color I wanted.

You should now have a solid color around your photo. To make it a little more interesting we will put a filter on the stroke. Select the magic wand tool
from the toolbar and click on the red stroke. You should have marching ants outlining the red stroke as shown below:
Now we will apply the filter. Select Filter > Texture > Texturize:
This will open the texture dialog box:

Try out what each texture does to the stroke by selecting it. After clicking through all the options I decided I liked the Mosaic Tiles for this photo. Click OK to close the Texture dialog box. this is my finished product: