background
barbed
black
blue
boundary
cage
chainlink
color
construction
crime
danger
day
escape
fence
forbidden
frame
freedom
horizontal
image
iron
isolated
mesh
metal
military
night
nobody
out
outdoors
pattern
prison
prisoner
private
protection
razor
safety
security
separation
sharp
sign
silhouette
single
sky
space
steel
system
wall
war
warning
white
wire