This picture is not a Photomontage, is the wonderful job of a professional photographer whose name is Margherita:
The explanation of this picture was given by Margherita itself to another user of Panoramio, i'm translating the part of the answer that we are interested in.
On a A3 format sheet create a face, with flowers or something else. The drop works as a lens, then remember to hung the image upside down more or less at 40 cm behind the drops.
The shutter speed must be very fast 1/6000-1/8000, use a very long focal that requires a lot of light, and possibly, shoot with sunlight in daytime or at night. Prepare an adjustable source of drops and sprinkle drops in 6 - 8 points. Shoot a serie of 50 poses and then change the scene, repeat the scene for another 20-25 times and then you'll see great results.
Thanks to Margherita for this precious tutorial.