Waterfall Reflections.

The final image:

The original two images.

1/. Open both the waterfall and over the top image.

2/. Remove the background from the over the top image.

2.1 Image Size.

2.2 File New/Transparent and the same size as the original image.

2.3 Copy/Paste the image to the new Transparent file.

2.4 Erase the background by using either: Eraser Tool, The Magic Wand Tool, the Rectangular Marquee Tool.

2.5 Use the Move Tool to position your image.

2.6 Copy/Paste the over the top image to the waterfall and use the Edit/Transform Tool to resize the image to the required size.

2.6 Move the image into its holding position.

2.7 Using the Opacity, drop back the image luminosity to a fade out.

 

3/. Go back to the over the top image and Image Rotation Flip Horizontally.

4/. Copy/Paste the over the top image, Edit/Free Transform, resize and place the image where required. Change the Opacity.

5/. Save the image as a .JPG.

Here's another version of a waterfall with a black and white image over the top.