Often our eyes need help to perceive the size of objects
Because framing is selective, there is always an element of abstraction in photographs. This can make it difficult to accurately judge the size of objects in an image. So, we occasionally need to include an object of a known size in the composition. This could be a person, building, car or any common object whose size we immediately understand.
Right Towering Iceberg in this image, the iceberg could be almost any size, from a few metres to several hundred metres; it is only when we notice the boat that we fully appreciate the size of the iceberg