On this Adorama video, pro photographer Joe McNally talks about demonstrating cale in an image.
Showing how big or small an object is in a an image isn’t as simple as you might think. If the purpose is just to demonstrate the size you can always use any familiar object with a known size that will help the viewer estimate the relative size of the object photographed. However, when shooting a carefully planned image which also needs to demonstrate scale – it is not always so simple.
McNally shows a few examples of how he was able to create the feeling of scale in some of his images without subtracting from their artistic look (hint: think about where you would like your relative sized object to be, what object will you use and how it is related to your main subject).