Silhouettes can pose a challenge when photographing them. You have to pay close attention to the available light or make your own. The studio is great for silhouette photography since you control all the aspects especially the lighting.
Silhouettes need not be of people, anything can be represented as a silhouette. Plants, leaves, rocks, vases, pets, people, houses..the list goes on, although translucent flowers or petals can be a mission. For this we collect some Silhouettes: 20 + Stunning Collections Of Vector Silhouettes
Silhouettes can also be used to set a romantic mood, such as couples in the beach. Special effects can be achieved in the studio by using a canvas with the subject behind it and light from behind. Use of color filters on the studio light can render silhouettes that are surrounded by a brilliant color, a technique often used in advertising campaigns.
A silhouette most dramatic effect, at least from my perspective, is that it opens the mind to various interpretations and lend themselves for a little mystery. Good luck and have fun