abstract
barbed
barbed wire
barbwire
barrier
blue
blur
border
boundary
bright
cloud
concept
confinement
copy
copyspace
danger
defense
division
escape
fence
forbidden
free
freedom
frontier
heaven
hope
isolation
liberty
metal
perspective
prison
protection
quarantine
release
right
safety
security
separation
shadow
sharp
silhouette
sky
space
steel
top
view
wall
wire
zone