As with the fake transparency method, open your background image and get a sample of it. With the eyedropper tool, sample what appears to be the dominant color - if it's a predominantly dark image, choose a dark part of the image. If it's a light background, choose a light part of the image.

Figure 12: Our new background to build our image on.

Once you have the sample color you need, create a new image with that color as the background or fill the background of a current image. Create the image as you wish, keeping in mind that it will eventually be displayed over top a background with the same dominant color as the background you've selected.

Figure 13: The final image with drop shadows applied.