You can find most of these backgrounds on these sites and galleries:
https://nijicollage.xyz/
https://e-hentai.org/g/2643697/84f1990232/
https://e-hentai.org/g/1508758/c4a5483dee/
https://e-hentai.org/g/1500697/900f12e375/
https://e-hentai.org/g/1324159/b9a475c665/
https://e-hentai.org/g/857500/5dd5d735cb/
https://e-hentai.org/g/753600/a5e808bc34/
https://e-hentai.org/g/340442/55524aed96/
https://e-hentai.org/g/1308063/5f1abb7925/
https://e-hentai.org/g/1294394/11d42d747b/
https://e-hentai.org/g/931872/2d0889e656/
https://e-hentai.org/g/932524/e514cf7d4f/
https://e-hentai.org/g/754952/78f574017e/
https://e-hentai.org/g/814004/f34f37f2a8/
https://e-hentai.org/g/922450/092cf027f6/
https://e-hentai.org/g/1471939/669d581d3c/
https://e-hentai.org/g/183437/a0453c032a/
https://e-hentai.org/g/1314472/4a3b0d9e3b/
https://e-hentai.org/g/1344869/4908b8f251/
https://e-hentai.org/g/1390755/c5fadff09b/
https://e-hentai.org/g/1311919/c071785bbb/
https://e-hentai.org/g/1294394/11d42d747b/
https://e-hentai.org/g/1224340/637ee8be21/
https://e-hentai.org/g/737791/23c53b32fb/
https://e-hentai.org/g/829174/1705672736/
https://e-hentai.org/g/991702/738f4f0f97/
https://e-hentai.org/g/932549/8226f9ae07/
https://e-hentai.org/g/857500/5dd5d735cb/
https://e-hentai.org/g/651740/afef8b1a75/
https://e-hentai.org/g/629748/2752932a2b/
https://e-hentai.org/g/1464151/0814d2cee7/
https://e-hentai.org/g/1445671/77d919bb30/
https://e-hentai.org/g/1145569/f70070777f/
https://e-hentai.org/g/837581/ae2b88145f/
https://e-hentai.org/g/669185/be5d7ec53b/
https://e-hentai.org/g/742902/1ca8997b1f/
https://e-hentai.org/g/1591399/a10adc4f29/
https://e-hentai.org/g/759744/1b5571ac30/
https://e-hentai.org/g/937719/630e7ae9ae/
https://e-hentai.org/g/762238/0082d8684e/
https://e-hentai.org/g/1334044/cda9702e03/
https://e-hentai.org/g/1690327/97dab6ac59/
https://e-hentai.org/g/1711383/aabae95bea/
https://e-hentai.org/g/1486107/bb13962ff8/
https://e-hentai.org/g/1507255/3f45d10346/
https://e-hentai.org/g/1498992/7fd63d6b80/
https://e-hentai.org/g/1464107/8ac2f015a9/
https://e-hentai.org/g/843558/db6bf16f94/
https://e-hentai.org/g/75096/1edcf3fbc2/
https://e-hentai.org/g/1321433/124fcbc5cb/
https://e-hentai.org/g/2226365/1eedcd12a5/
https://e-hentai.org/g/1492324/85c29f0e15/

求个种子

Base +6, WisteriaBerlitz +6

Oh, cool, this is actually useful.

Base +32, diggerlover +12, EM1K04 +6, meow_pao +59, suratkabar +24, xXtestingXx +7, billyland +7, MehMeher +10

sorry错看成了backroom😂吓我一跳

Base +5

What are the usage rights on these? can I put them in Forkheads' flash games?

Base +8, Azzy -10, hikasa +9

@Joshex every linked gallery I checked is a commercially sold game, surely these backgrounds can't be used in anything you'd sell. Some personal project, sure

Base +6, Yappachino +1, Harvest13 +8, MehMeher +10, RespectfulLurker +5, hikasa +9

我就想知道河豚屋是彻底转型了吗，怎么不做主业跑这里来了

Base +6

This is actually major league cool. Any chance we can get a list of what games each set of backgrounds is from? Or if they were reused and such?

Base +7, Azzy +10