Firstly, let me say this: this mod would not have been possible without the incredible artwork created by all of these amazingly talented artists. Over a year ago I had an idea for a Stellaris mod that LastLeviathan was kind enough to help me set up. Since then, the collection of backdrops has grown substantially. Last month, in preparation for the 2.0 Cherryh / Apocalypse update, I decided it was high time to give credit where credit was due and create a comprehensive list of the artworks we used.

Where possible, I've tried to link directly to the files we used as a basis for the backdrops. When I started collecting the art, I did not record these URLs, so if you're looking for a specific piece of art, simply visit the artists' Artstation or DeviantArt page and you are bound to find what you were looking for.

Again, all credit goes to the creators of the artwork. We simply used what was freely available to us on the internet. If any of the people listed here feel that their artwork has been used inaproppriately, feel free to contact LastLeviathan or myself and we will see that it is properly removed.

Diverse Rooms
"apocalyptic1_room" = {Emmanuel Shiu}
"apocalyptic2_room" = {Maciej Wojtala}
"apocalyptic3_room" = {Maciej Wojtala}
"apocalyptic4_room" = {Maciej Wojtala}
"apocalyptic5_room" = {mechanickalmind}
"apocalyptic6_room" = {Ryan Church}
"apocalyptic7_room" = {Adam Burn}
"apocalyptic8_room" = {Jesse van Dijk}
"apocalyptic9_room" = {Sergey Vasnev}
"apocalyptic10_room" = {Dorje Bellbrook}
"apocalyptic11_room" = {Ryan Church}
"apocalyptic12_room" = {Kentaro Kanamoto}

"barren1_room" = {Andree Wallin https://andreewallin.deviantart.com/art/Alien-landscape-105953893}
"barren2_room" = {Martin Deschambault https://www.artstation.com/artwork/9merL}

"cave1_room" = {Geoffroy Thoorens / Emmanuel Shiu}
"cave2_room" = {Little Water Studio}
"cave3_room" = {Piotr Dura}
"cave4_room" = {Ishtaure Dawn}
"cave5_room" = {Concept art from Starcraft II - unknown creator http://eu.battle.net/sc2/en/blog/10050519/starcraft-ii-creative-development-qa-part-8-10-12-2012}
"cave6_room" = {Graven Tung}
"cave7_room" = {John Wallin Liberto}
"cave8_room" = {Reddit thread: https://www.reddit.com/r/EarthPorn/comments/2183km/sunrise_from_atop_the_zugspitze_germany_1835x2000/cgatybw/}
"cave9_room" = {Phuoc Quan https://nkabuto.deviantart.com/art/Underground-City-252942700}
"cave10_room" = {Concept art from Starcraft II - unknown creator}
"cave11_room" = {Alex Ruiz}

"cityscape1_room" = {Emmanuel Shiu}
"cityscape2_room" = {Hideyoshi http://hideyoshi.deviantart.com/art/Megastructure-79888020}
"cityscape3_room" = {Paul Chadeisson / Michel Koch https://www.videogamesartwork.com/games/remember-me/city-design-10}
"cityscape4_room" = {James Paick https://www.artstation.com/artwork/Xa9La}
"cityscape5_room" = {Mikhail Rakhmatullin}
"cityscape6_room" = {Xiaohui Hu}
"cityscape7_room" = {Khang Le}
"cityscape8_room" = {Janos de Ro http://jonasdero.deviantart.com/art/Celestia-531585695}
"cityscape9_room" = {Concept art from Star Wars: The Old Republic - Alderaan http://www.swtor.com/info/media/concepts/alderaan}
"cityscape10_room" = {Christian Hecker}
"cityscape11_room" = {Wojtek Fus https://www.artstation.com/artwork/wO2GV}
"cityscape12_room" = {Concept art from Prey 2 - unknown creator}
"cityscape13_room" = {mrrainbowwj https://mrainbowwj.deviantart.com/art/Sci-fi-Buildings-482679963}
"cityscape14_room" = {unknown - unable to find source}
"cityscape15_room" = {Dmitriy Kuzin - https://rulez-dmitriy.deviantart.com/art/oasis-545112790}
"cityscape16_room" = {Bastien Grivet - https://grivetart.deviantart.com/art/Big-Sun-City-327327438}
"cityscape17_room" = {Alpha Step}
"cityscape18_room" = {Tigaer}
"cityscape19_room" = {B. Börkur Eiríksson}
"cityscape20_room" = {Emmanuel Shiu}
"cityscape20_room" = {James Paick}
"cityscape21_room" = {James Paick}
"cityscape22_room" = {grivetart}
"cityscape23_room" = {Kevin Jick}
"cityscape24_room" = {Luciano Neves}
"cityscape25_room" = {Martin Deschambault}

"command1_room" = {Nicolas Ferrand}
"command2_room" = {Alexey Yakovlev}
"command3_room" = {Ryan Church https://robertsspaceindustries.com/comm-link/transmission/13097-Idris-Corvette-Revealed}
"command4_room" = {Ryan Church}
"command5_room" = {TheArtofSaul https://theartofsaul.deviantart.com/art/Alinias-Interior-401801798}
"command6_room" = {Ryan Church}
"command7_room" = {Ryan Church https://spacestationwagon.com/2016/05/06/revenge-of-the-fifth-the-episode-iii-concept-art-of-ryan-church/}
"command8_room" = {Tobias Roetsch / ChrisCold https://gtgraphics.de/en/wallpapers/any-direction}

"control1_room" = {Jabril Graves https://codepen.io/Treatise/pen/NrWzjd}
"control2_room" = {Donglu Yu}
"control3_room" = {BlueRogueVyse http://blueroguevyse.deviantart.com/art/Sci-Fi-Interior-434560102}

"desert1_room" = {Ryan Church}
"desert2_room" = {meckanicalmind}
"desert3_room" = {Martin Deschambault}
"desert4_room" = {Martin Deschambault}
"desert5_room" = {Joakim Olofsson}
"desert6_room" = {Brad Wright}
"desert7_room" = {Daria Ridel}
"desert8_room" = {Martin Deschambault}

"ethic_light_side_room" = {Screenshot from Star Wars: The Old Republic - Tython Jedi Temple http://starwars.wikia.com/wiki/File:Temple_Interior.png }
"ethic_light_side2_room" = {Tony Weinstock}

"ethic_dark_side_room" = {Concept art from Star Wars: The Old Republic - Sith Ship http://swtor.wikia.com/wiki/File:CA_Sith_Ship01_full.jpg}
"ethic_dark_side_room2" = {BigT http://www.scifi-meshes.com/forums/showthread.php?80354-The-Star-Wars-Project/page8}
"ethic_dark_side_room3" = {Doug Chiang http://www.slashfilm.com/we-may-be-heading-back-to-darth-vaders-castle-in-upcoming-star-wars-movies/}

"frozen1_room" = {Edvige Faini http://conceptartworld.com/artists/edvige-faini/}
"frozen2_room" = {Peter Popken}
"frozen3_room" = {Anna Shulgina https://anekashu.deviantart.com/art/ice-planet-399175570}
"frozen4_room" = {artofjokinen}
"frozen5_room" = {Jadrien Cousens}
"frozen6_room" = {Kentaro Kanamoto}

"fungus1_room" = {Shahab Alizadeh https://shahabalizadeh.deviantart.com/art/Sector-23-442398225}
"fungus2_room" = {Alexiuss http://alexiuss.deviantart.com/art/Spores-442378595}
"fungus3_room" = {Chenthooran http://www.deviantart.com/art/Alien-Landscape-480109336}
"fungus4_room" = {MeckanicalMind http://meckanicalmind.deviantart.com/art/Alien-Jungle-357794603}
"fungus5_room" = {Quentin Stipp https://www.artstation.com/artwork/aoGD9}
"fungus6_room" = {Dorje Bellbrook https://www.artstation.com/artwork/2xOqg}
"fungus7_room" = {Martin Deschambault}

"gaia1_room" = {Seth Engstrom}
"gaia2_room" = {artofjokinen}
"gaia3_room" = {Jonas Dero}

"hive1_room" = {Noah Stacey https://stingerbee85.deviantart.com/art/Reclamation-Pool-110846749}
"hive2_room" = {Luke Mancini https://mr--jack.deviantart.com/art/Egg-Caves-258873559}
"hive3_room" = {David Levy http://conceptartworld.com/news/enders-game-concept-art-by-david-levy/}
"hive4_room" = {Ryan Church http://conceptartworld.com/news/transformers-2-concept-art-by-ryan-church/}
"hive5_room" = {Ryan Church http://ryanchurch.com/dead-space/}
"hive6_room" = {Ryan Church http://ryanchurch.com/dead-space/}
"hive7_room" = {David Levy http://conceptartworld.com/news/enders-game-concept-art-by-david-levy/}
"hive8_room" = {Alpha Step}
"hive9_room" = {Ryan Church}

"human1_room" = {Sparth https://www.artstation.com/artwork/QraPr}
"human2_room" = {Viktor Jonsson}
"human3_room" = {David Levy}
"human4_room" = {Igor Vitkovskiy}
"human5_room" = {Eric Persson http://www.ericpersson.se/?page_id=254#}
"human6_room" = {David Levy http://conceptartworld.com/news/enders-game-concept-art-by-david-levy/}

"imperium1_room" = {unknown artist, Warhammer 40K art}
"imperium1_room" = {Richard Knight}

"industrial1_room" = {James Paick https://www.artstation.com/artwork/Lab65}
"industrial2_room" = {Fabio Barretta Zungrone https://www.artstation.com/artwork/BeN9}
"industrial3_room" = {Kentaro Kanamoto http://korbox.cgsociety.org/art/buildings-photoshop-smoke-soldiers-ground-breathe-975277}
"industrial4_room" = {Camille Kuo https://tavenerscholar.deviantart.com/art/interior-colored-195913614}
"industrial5_room" = {Brian Sum https://app.artstation.com/artwork/W88G}
"industrial6_room" = {Gia Nguyen https://gunsbins.deviantart.com/art/Industry-zone-concept-212580765}
"industrial7_room" = {Sarichev}
"industrial8_room" = {Xiaohui Hu https://xiaohui.artstation.com/projects/064RK}
"industrial9_room" = {Joao Silva}
"industrial10_room" = {theartofsaul}
"industrial11_room" = {Dorje Bellbrook}
"industrial12_room" = {Dorje Bellbrook}
"industrial13_room" = {James Paick}
"industrial14_room" = {Gia Nguyen}
"industrial15_room" = {Dominique Velsen}
"industrial16_room" = {theartofsaul}

"masseffect_room" = {droot1986 - http://droot1986.deviantart.com/art/Mass-Effect-2-Citadel-154770894}
"masseffect2_room" = {unknown creator}

"mech1_room" = {Bondhan Kimbalazani http://www.bondhan.com/hangar.html}
"mech2_room" = {Dennis Chan https://www.artstation.com/artwork/DdJA}
"mech3_room" = {John Wallin Liberto}
"mech4_room" = {John Wallin Liberto}
"mech5_room" = {Stephan Martiniere}
"mech6_room" = {Khang Le}
"mech7_room" = {Phuoc Quan https://nkabuto.deviantart.com/art/Alien-Planet-Explorers-377010856}
"mech8_room" = {Jesse van Dijk}

"militarist1_room" = {Adam Burn}
"militarist2_room" = {artofjokinen}
"militarist3_room" = {Adam Burn}
"militarist4_room" = {Adam Burn}
"militarist5_room" = {theartofsaul}
"militarist6_room" = {Paul Chadeisson}
"militarist7_room" = {Jeffrey Rex}
"militarist8_room" = {Nick Foreman}
"militarist9_room" = {Edouard Groult}
"militarist10_room" = {unknown creator}
"militarist11_room" = {Jim Hatama}
"militarist12_room" = {Jesse van Dijk}

"outdoor1_room" = {Stellaris loading screen}
"outdoor2_room" = {Stellaris loading screen}
"outdoor3_room" = {Ling Xiang http://conceptships.blogspot.nl/2012/09/concept-environments-with-ships-by-ling.html}
"outdoor4_room" = {Kentaro Kanamoto http://korbox.cgsociety.org/art/sci-fi-photoshop-spaceship-canyon-unknown-893357}
"outdoor5_room" = {Kang Le}
"outdoor6_room" = {Victor Boza https://ecsian.deviantart.com/art/Alien-planet-base-408653024}
"outdoor7_room" (Ryan Bliss}
"outdoor8_room" = {Andree Wallin}
"outdoor9_room" = {Wojtek Fus https://www.artstation.com/artwork/eQbPZ}
"outdoor10_room" = {Erik Schumacher https://erikshoemaker.deviantart.com/art/Prometheus-326743531}
"outdoor11_room" = {unknown creator https://alpha.wallhaven.cc/wallpaper/110884}
"outdoor12_room" = {Kentaro Kanamoto https://korbox.deviantart.com/art/Distant-amber-271755733}
"outdoor13_room" = {Wojtek Fus https://www.artstation.com/artwork/QPkvZ}
"outdoor14_room" = {Luke Mancini https://mr--jack.deviantart.com/art/Frozen-Hive-258872955}
"outdoor15_room" = {Ryan Church}
"outdoor16_room" = {Seokin Chung}
"outdoor17_room" = {Shahabalizadeh}
"outdoor18_room" = {Tigaer}
"outdoor19_room" = {Kentaro Kanamoto}
"outdoor20_room" = {Kentaro Kanamoto}
"outdoor21_room" = {Martin Deschambault}

"plantoid1_room" = {Herve/groussin NURO-art https://nuro-art.deviantart.com/art/Avatar-158126254}
"plantoid2_room" = {Seth Engstrom http://4.bp.blogspot.com/_FakyimrdCyQ/TNYhQ-Of1xI/AAAAAAAAAvg/Oyo38KSlCv4/s1600/WillowTreesFinalPrint2.jpg}
"plantoid3_room" = {RichardDorran http://richarddorran.deviantart.com/art/Enchanted-Forest-306742874}
"plantoid4_room" = {Narandel http://narandel.deviantart.com/art/Elementium-Forest-Concept-02-421622529}
"plantoid5_room" = {ImSkeptical http://imskeptical.deviantart.com/art/Crash-Landing-459354564}
"plantoid6_room" = {Vitaliy Ratushnyak https://vityar83.deviantart.com/art/dark-forest-299891639}
"plantoid7_room" = {Ryan Church}
"plantoid8_room" = {Ryan Church}
"plantoid9_room" = {Dorje Bellbrook}
"plantoid10_room" = {Alyn Spiller}

"robotic1_room" = {Alex Ruiz}
"robotic2_room" = {Alex Ruiz}
"robotic3_room" = {Alex Ruiz}
"robotic4_room" = {Alex Ruiz}
"robotic5_room" = {Alex Ruiz}
"robotic6_room" = {Alex Ruiz}
"robotic7_room" = {Alex Ruiz}
"robotic8_room" = {Alex Ruiz}
"robotic9_room" = {Ryan Church}
"robotic10_room" = {Alex Ruiz}
"robotic11_room" = {Jose Arias}

"spiritualist1_room" = {Max Bedulenko}
"spiritualist2_room" = {Franklin Chan, possibly wrongly attributed}
"spiritualist3_room" = {Marvin Herbring - https://www.artstation.com/artwork/dKg0w}
"spiritualist4_room" = {Sebastian Wagner}
"spiritualist5_room" = {Quentin Stipp}
"spiritualist6_room" = {Thomas Chamberlain}
"spiritualist7_room" = {Alexandr Merentiev}
"spiritualist8_room" = {Marc Simonetti}
"spiritualist9_room" = {Christopher Balaskas}
"spiritualist10_room" = {JJCanvas}

"tech1_room" = {James Clyne}
"tech2_room" = {Gia Nguyen http://gunsbins.deviantart.com/art/underground-186547967}
"tech3_room" = {Ryan Church http://ryanchurch.com/dead-space/}
"tech4_room" = {Roderick Wong https://roderickwong.files.wordpress.com/2012/08/ms5_skrull_interior_maincentralspire_rod1.jpg}
"tech5_room" = {Sergey Samarskiy http://mikrob.cgsociety.org/art/lab-photosho-science-environment-design-concept-art-total-domination-1199107}
"tech6_room" = {Maciej Wojtala https://m-wojtala.deviantart.com/art/Spaceship-interrior-211932225}
"tech7_room" = {Ryan Church http://ryanchurch.com/dead-space/}
"tech8_room" = {Joe Peterson https://www.artstation.com/artwork/e0eWP}
"tech9_room" = {Luis Calero}
"tech10_room" = {Stephan Martiniere}
"tech11_room" = {Alex Chin Yu Chu http://alexchu.squarespace.com/portfolio/halo-reach/5719201}
"tech12_room" = {Franklin Chan}
"tech13_room" = {Gia Nguyen https://gunsbins.deviantart.com/art/Glass-house-concept-228223581}
"tech14_room" = {Martynas}
"tech15_room" = {Alpha Step}
"tech16_room" = {Leon Tukker} https://www.artstation.com/artwork/the-rundowns

"throne1_room" = {Ryan Church http://ryanchurch.com/john-carter-of-mars/}
"throne2_room" = {Thiago Klafke}
"throne3_room" = {Joey Studz}
"throne4_room" = {Ryan Church http://ryanchurch.com/john-carter-of-mars/}
"throne5_room" = {Alex Ruiz https://alexruizart.deviantart.com/art/Abandoned-Alien-Ruins-191297204}
"throne6_room" = {Floyd Billingly}
"throne7_room" = {Samuel Santos https://www.artstation.com/artwork/lRPXV}
"throne8_room" = {Thiago Klafke}
"throne9_room" = {Khang Le}
"throne10_room" = {Ryan Church}
"throne11_room" = {Julian Faylona}

"toxic1_room" = {Maxim Buyanov https://www.artstation.com/artwork/kDKY82}
"toxic2_room" = {Jason Park https://www.artstation.com/artwork/VdAgR}
"toxic3_room" = {Jakub Koslowski https://www.artstation.com/artwork/k4WBVx}
"toxic4_room" = {Jakub Koslowski https://www.artstation.com/artwork/k4WBVx}

"trader1_room" = {Devon Fay}
"trader2_room" = {Ryan Church}

"underwater1_room" = {Phuoc Quan https://nkabuto.deviantart.com/art/Underwater-City-253787721}
"underwater2_room" = {Chenkai (only reference found here: https://pinterest.com/pin/286330488781755152/ Link is dead}
"underwater3_room" = {Andrea Susini https://io9.gizmodo.com/gorgeous-art-shows-what-life-would-be-like-in-cities-be-1556782450}

"stargate1_room" = {Dorje Bellbrook}

"xenomorph_room" = {Unknown creator - 'Xenomorph Hive' Google image search}
"xenomorph2_room" = {Brad Wright http://conceptartworld.com/news/alien-isolation-concept-art-by-brad-wright/}
"xenomorph3_room" = {Marek Okon https://www.artstation.com/artwork/qQvKD}

Edit - 22-11-2021
For the Aquatics / 'Herbert' 3.2 update for Stellaris, the following rooms were added:

"underwater4_room" = {Tomas Muir https://www.deviantart.com/parkurtommo/art/Spider-Lair-481763497}
"underwater5_room" = {Caffe Tylo https://www.artstation.com/artwork/3eAv}
"underwater6_room" = {Naeun Yang https://www.artstation.com/artwork/aRRdPR} (recommended by Eona)
"underwater7_room" = {Noah Bradley https://www.deviantart.com/noahbradley/art/May-Sketch-a-Day-2020-2-840236399}
"underwater8_room" = {Noah Bradley https://www.deviantart.com/noahbradley/art/Teach-Me-the-Angel-s-Song-585854608} (recommended by Eona)
"outdoor23_room" = {Noah Bradley https://www.deviantart.com/noahbradley/art/To-Feel-the-Edge-of-Heaven-592521480}
"outdoor24_room" = {Thomas Wievegg https://www.deviantart.com/thomaswievegg/art/Orbital-Horror-626606707}
"frozen7_room" = {Thomas Wievegg https://www.deviantart.com/thomaswievegg/art/Nexus-732543154}
"hive12_room" = {Thomas Wievegg https://www.deviantart.com/thomaswievegg/art/Belly-of-the-Beast-741744636}