I've used Photoshop CS5 Extended for my screen shots, but you should be able to follow the tutorial in older versions of Photoshop and Photoshop Elements. Differences in Photoshop Elements are also noted where appropriate.
First open the photo you want to work with. I will assume you have already cropped and performed any desired touch-ups on the photo.
If the layers palette only shows a background layer, you will need to promote the background to a layer. To do this, double click on the word "Background" on the layer in the Layers palette, then in the New Layer dialog, name the layer "Photo."
Before creating the mat effect, you will need to increase the canvas area around the photo. We can do this with the crop tool. Select the crop tool and drag a crop area that covers the whole photo. Then drag the corner handles of the crop area outside of the photo's boundaries. You do not have to be exact at this stage, but you should allow enough room for your mat effect and a drop shadow.
When you commit the crop, the canvas will expand around the photo to create extra space.
If you've never used the crop tool in this way and are having trouble, see the following lessons:
• Photoshop Crop Tool Lesson | Practice Exercises
• Photoshop Elements Crop Tool Lesson | Practice Exercises
