abstract
backdrop
background
barrier
black
border
chain
chained
closeup
design
detain
dimensional
enclose
enclosure
fence
grate
gray
grey
grid
grunge
iron
isolated
jail
keep
lattice
link
linkage
mesh
metal
metallic
net
pattern
penal
prison
prisoner
rusty
security
shape
sharp
silhouette
steel
strong
system
texture
tile
wall
white
wire