Back in 2013, Google image search was very powerful we could reverse search everything that was photoshopped, trased or cropped to reach to the original source.
Like this /g/610127/9377294bb3/ (see the comment section below)
But then they decided to nerf it into the ground. There are some alternative services such as IQDB but they are nowhere near as good as google image search in prime I still really missed it.

Edit: ok, i tried (for science). turns out that was not that bad. the technology was weakened, yet still there.
#2-9 /s/1bc3447336/811713-105 [HERENCIA] Relaxation Yuka En
#10-20 /s/39df92a29f/1092734-1699 [CLOCKUP] Kenzen! Hentai Seikatsu no Susume
#21-28 /s/7935fbc220/724946-127 [Orcsoft] Kanojo wa Dare to demo Sex suru
#29-36 /s/19af8a30c5/640324-783 [Tsurumiku] Yume Kui
#37-54 /s/4448d976ce/927137-188 [Pin-Point] Tsuiraku Jinsei
#55-65 https://gelbooru.com/index.php?page=post&s=view&id=3322964 [Lilith] Taimanin Asagi Battle Arena
#66-73 /s/7a37a9b695/1000443-416 [SILKY'S SAKURA] Mama no Oppai
#74-94 /s/170fcd23dc/709358-79 [Pin-Point] Inshitsu Otaku ni Ikareru Imouto
#101-110 /s/6fd8a93169/1067427-26 [ANIM.teamMM] Tsuma no Nikuana ni Homestay Suru Macho Ryuugakusei
#111-120 /s/82a6558364/1067427-477 [ANIM.teamMM] Tsuma no Nikuana ni Homestay Suru Macho Ryuugakusei
#121-128 /s/9915630350/900206-509 [ALICESOFT] Tsumamigui 3
#129-138,153-161 /s/83a78dce6a/1092739-55 [Studio Ubai] Psy-min Appli
#145-152 /s/a43bb45e67/722241-1097 [Clock Up] Fraternite
#162-169 /s/a638fcc111/972506-63 [PakoPako Soft] Pako ★ Shisu
#170-178 /s/7bc1be0269/984732-80 [HERENCIA] Relaxation Yuka M
#179-184 /s/60ddc7883b/984732-23 [HERENCIA] Relaxation Yuka M
#185-193 /s/54ece5165f/724946-185 [Orcsoft] Kanojo wa Dare to demo Sex suru
#194-208 /s/577510773c/1024149-101 [ALICESOFT] Heartful Maman
#209-226 /s/11e627de3e/1092734-1039 [CLOCKUP] Kenzen! Hentai Seikatsu no Susume
#236-244 /s/7c29cebf02/929250-132 [Studio Charen] Houkago Saimin Club 3
#245-253 /s/d59105c5e4/935278-248 [Atelier Sakura] Kashidashi Tsuma, Marina no Netorase Houkoku Gaiden 1
#256 /s/3cd2b2c05c/974001-139 [Bishop] Mesu Kyoushi 4
#257 /s/df1b91be27/974001-1214 [Bishop] Mesu Kyoushi 4

Last edited on 22 September 2017, 16:58 UTC.

Base +11, jinkjink -6, xz8885 +6, TheOldDeus +6, Mrsuperhappy +29, zexalarcv123 +4, Laharl_EAC +10, yuuuuuuoi +6, jeeyi12 +6, plaquebringer +6, Refyrsen +6, illusioninusall +15, ROBERTO2109 +6, and 10 more...

只有沙希才是纯爱

Base +5, zexalarcv123 +4, MG1937 +3, 國王男孩 +5, a912654473 +6

支持！~

Base +6, nsholic +6

拿别的图p个脑袋上去……何必呢

Base +8, rex31 -5, abcd98328 +5, xz8885 +6, tom19970526 +3, err-404 -1, yzw1635994342 +2, Alex_viktor +4, DDDD11a -5, yjj163419 +3, REcount -20, kaname_madoka -7, Wuke. +5, and 4 more...

for science! you've done we'll pal

Base +6, zexalarcv123 +4, plaquebringer +6, Ceon +6, Refyrsen +6, ROBERTO2109 +6, AwesomeArk +5

真是满满的爱

Base +6, zexalarcv123 +4

这种玩意真有人看?给半星都嫌多

Base +6, nsholic -6, a912654473 -6, Lmx1999 -6, ysbwbwyshs -5, Wuke. +5

P图的功力确实可以。献媚的雪乃杀伤力真的很强

Base +6

说实话，不喜欢，人物比例不协调，实在看不下去。。。

Base +2