Silhouette
Silhouette /ˌsɪl.uˈet/ (noun)
a dark shape on a light background, shadowed contour, outline, shape, shadow, profile, figure:
The silhouette picture on the wall scared the hell out of all in the party.
If you hadn’t taken the picture against the sun, it wouldn’t have been a silhouette with a disguised object in front of it.
During the turbulent condition, the protesters removed many pictures of the recent mayor drawn in silhouette on the walls.
Silhouette sign is a radiologic term and it happens when there is mass inside the lungs that covers the borders of heart and we couldn’t make out the borders of the heart clearly.
So, it’s a technical term.