Drop Shadows: Prep Your Photo
To get started, open a photo in Photoshop Elements. Make any changes you want--tweak the colors and exposure, for example--and then crop the image to your satisfaction.
Because the drop shadow effect is designed to work on a layer, you need to promote your photo to layer status. To do that, find the Layers palette on the right side of the screen and double-click the image, which should be identified currently as 'Background'. The New Layer dialog box will appear. Click OK. Your image is now a layer, indicated by the name 'Layer 0' in the Layers palette.