Open the image and make a rectangular selection around the top part of the image, just above the horizon line.

Press Control+R to crop.
Save as 1.jpg to your desktop folder. Minimize PI.
Open the Water Reflet folder on your desktop open the reflet folder and click on the Reflet file, click yes to run.
Click the Yellow Folder on the left top part of the program and browse to your 1.jpg and open it.
Use these settings:

Images: 5 Hauteur (height)%:50% Perspective ticked. Click
the Options button and
click: Animation. Click Options: Vitesse: Lente. (Speed: Slow). Click Options once more: Type de vague -(type of waves): Court (short).
Click on Fichier (File): Exporter (Export). A new box will open, please use these settings.

Animated gif - only the reflet - 256 colors and click OK. Click No in the next box as we don't want
to save the animation as a webpage and save as 1.gif to the folder on your desktop. You may close the Reflet program.
Open your Gif Animator, browse to your desktop folder and open the 1.gif we just made. File save as: UFO, save as 1.ufo to your desktop folder.
Close Gif Animator.
Maximize your PI and open the 1.ufo file. You should have 2 files open at this stage. The cropped top part of the painting and the
1.ufo containing 5 layers. (your reflet). Activate the top part image, press Shift+N to expand your canvas. Expand the bottom of your canvas
with as much pixels as the height of your reflet objects. My reflet is 137 pixels high. Yours may be different, depending how much you cropped
your painting in the first step of this tutorial.

Make your reflet (1 ufo) active, in your Layer Manager select the bottom layer (not the base image) with the name Obj -1. Copy.
Make your top image active and: Paste. Right click: Align - Bottom. In your Layer Manager rename this layer as Frame 1.