A lot of now unused images have been removed. I checked the file you mentioned and it doesn't use that image at all.
Let me know if you encounter a missing image error in the game and where, and I'll look into it.
I've fixed the question typo for the next version, thank you.
Viewing post in Yuri University v0.60 now available! comments
at least "bg masturbate pillow (22)" is used and can be reached in a legal play-through w/o shenanigans , the reason I noticed it (and started the linter to take a more systematic look): Riding pillow -> Nude -> Scarlet joins -> 'Do you want to join me'. renpy tries (and fails) to load it in masturbation_new.rpy:311.
and seriously: lint is your friend :D