© Ralph A. Clevenger/CORBIS
This is an awesome image realized by the Nature Photographer Ralph A. Clevenger. It is very famous for its immediate impact and because it is the perfect explanation of the "Tip of the Iceberg" rule:
Because the density of pure ice is about 920 kg/m³, and that of sea water about 1025 kg/m³, typically only one-tenth of the volume of an iceberg is above water. The shape of the remainder under the water can be difficult to surmise from looking at what is visible above the surface. This has led to the expression "tip of the iceberg", generally applied to a problem or difficulty, meaning that the visible trouble is only a small manifestation of a larger problem.
However, while it is a realistic image, it's not properly a true photograph (it would have been impossible) but rather a digital composed image as it's perfectly explained by the author:
"The iceberg image is a digital composite that I designed to illustrate the concept of "what you see is not necessarily what you get". As an underwater photographer I knew that my "vision" of what a big iceberg looks like was impossible to get in reality so I had to create it. The image exists in nature but due to water visibility is not possible to capture on film. There are 4 separate images involved; the sky, the background, the top iceberg (shot in Antarctica), and the underwater iceberg (shot above water in Alaska and flipped in the final composite)."