Original graphics copyright Ronny Wester
Includes unmodified graphics and derived ones, licensed under CC-BY

Full list:

drains/0.png
barrel.png
barrel_blue.png
barrel_blue_wreck.png
barrel_skull.png
barrel_wood.png
barrel_wood_wreck.png
beam_8x8.png
beam_yellow_8x8.png
bench.png
bench_wreck.png
bigpanel.png
bloodstain.png
blueprint.png
bone_blood.png
bookshelf.png
bottle.png
bottle_orange.png
box.png
box_metal_green.png
box_metal_green_wreck.png
box_gray.png
box_green.png
box_red.png
box_wood.png
box_wreck.png
box2.png
bulletmarks.png
bullet_ball.png
cabinet.png
cabinet_wreck.png
cd.png
chair.png
chair_wreck.png
chars/body_arms_legs_16x16.png
chars/death_16x22.png
chars/guns/blaster_20x20.png
chars/guns/knife_16x20.png
chars/heads/bob_10x10.png
chars/heads/bugeye_10x10.png
chars/heads/cyberjones_10x10.png
chars/heads/cybersmith_10x10.png
chars/heads/cyberwar_10x10.png
chars/heads/cyborg_10x10.png
chars/heads/dragon_10x10.png
chars/heads/freeze_10x10.png
chars/heads/goggles_10x10.png
chars/heads/grunt_10x10.png
chars/heads/ice_10x10.png
chars/heads/jones_10x10.png
chars/heads/lady_14x10.png
chars/heads/madbugeye_10x12.png
chars/heads/ogre_10x10.png
chars/heads/ogreboss_10x14.png
chars/heads/professor_10x10.png
chars/heads/robot_10x8.png
chars/heads/smith_10x10.png
chars/heads/snake_10x10.png
chars/heads/warbaby_10x10.png
chars/heads/wolf_10x10.png
column.png
disk1.png
disk2.png
disk3.png
door/alien/
door/blast/
door/dungeon/
door/office/
egg.png
egg_wreck.png
exits/hazard/
exits/plate/
fireball_21x21.png
flame_14x15.png
folder.png
gas_cloud_24x21.png
goo.png
grenade_8x8.png
holo.png
keys/cube/
keys/dungeon/
keys/office/
keys/plain/
logo.png
mine_active.png
mine_inactive.png
molotov.png
paper.png
particles/blood0.png
particles/blood1.png
particles/blood2.png
particles/spark_classic.png
pci_card.png
plant.png
plant_wreck.png
radio.png
rocket.png
rocket_wreck.png
sack.png
safe.png
safe_wreck.png
scratch.png
skull.png
statue_ogre.png
table_clothed.png
table_lab.png
table_steel.png
table_wood.png
table_wood_candle.png
table_wood_wreck.png
terminal.png
tile/biggrid/
tile/checker/
tile/dirt/
tile/grid/
tile/flat/
tile/recessed/
tile/slab/
tile/smallsquare/
tile/stone/
tile/tile/
tree.png
tree_autumn.png
tree_autumn_wreck.png
tree_dead.png
tree_dead_wreck.png
tree_wreck.png
wall_goo.png
wall_skull.png
wall_stuff.png
wall/brick/
wall/carbon/
wall/granite/
wall/plasteel/
wall/steel/
wall/steelwood/
wall/stone/