PGHShutter

There's a multitude of ways to do this, but if you are using Photo and just need a solid line around your image, click on the layer image and right-click on the image, select layer effects from the pop-up menu, select Outline from the effects window, select your options for the outline (Alignment inside, color black, fill color solid, color black, etc). Fill style "contour" is a nice effect too. Hope this helps.