The painting "INRI" is part of the Carpi Diocesan Museum's "Gratia Plena" exhibition, which is currently on display in a church in the northern Italian town of Carpi.
Artist Andrea Saltini shows the naked body of Jesus after the crucifixion, as can be seen in a photo published on Monday on the online blog "Bussola Quotidiana".
Jesus' genital area is covered by the head of another man, giving the impression of oral sex.
During an on-site visit, a guide explained that the other man is the Roman officer Longinus, who is breaking Jesus' rib, wrote "Bussola Quotidiana".
In fact, the man in the painting is pressing his left hand against Jesus' ribcage.
The conservative blog accused the painting of blasphemy and demanded an explanation from the diocese of Carpi and Bishop Erio Castellucci.
The announcement of the exhibition opening last Saturday could be found on the diocese's website.
It said that the exhibition, which features around 20 pictures, shows Saltini's personal search for spirituality and invites visitors "to an experience of deep contemplation and confrontation".