The image next to the title is even from the Blacksad game so inspired by is definitely underselling it.
Indeed.
The character 'paper doll' art used in the dialogue scenes looks like painted over assets from the Blacksad game. Either someone took actual in game screenshots, or found the ripped models online and imported and posed them in Source Filmmaker or something similar, then used that as the basis for their artwork. Most likely using it as a background layer in some digital art program (Photoshop, GIMP, CorelDraw, etc.) and digitally painting over it. \
I honestly think the former rather than the later, because if they were using ripped and posable game assets, then why would they rotoscope real porn for the lewd art? Yeah, that art with the kitty lady getting plowed in missionary? Almost certainly that used real porn, rather than the Blacksad models, as its basis. Just look at her paper doll art in the other screenshot, the proportions for her head don't match. Her earrings have shrunk to half their size, and her ears themselves are the wrong shape and in the wrong position. That's partially why it looks way different. Or at least, it is quite noticeable if you have an eye for these kind of details.
Heck, all of the background locations look like they've had about half a dozen Photoshop filters layered over them to disguise their origins. So I'm not familiar enough with the game to gauge if they're (once again) using in game screenshots from the Blacksad game or just some appropriate stock photography, but there you go.