Dude... it's Judith with the head of Holofernes. For people who hate Christianity so much some of you guys know very little about it.
Actually, the other posters were right, the painting for None So Vile is Herodias' daughter holding the head of John the Baptist. There's no record of a platter in the bible regarding Judith, but there is one for the NT story:
"On Herod's birthday the daughter of Herodias danced for them and pleased Herod so much that he promised with an oath to give her whatever she asked. Prompted by her mother, she said, "Give me here on a platter the head of John the Baptist." The king was distressed, but because of his oaths and his dinner guests, he ordered that her request be granted and had John beheaded in the prison.
His head was brought in on a platter and given to the girl, who carried it to her mother. "
~Matthew 14:6-12
Also, here's an old interview with Jon Levasseur
"CoC: On _None So Vile_ there was a classical art influence on the packaging [the cover is Herodias with the head John the Baptist by Elizabeth Sirani -- Paul]; who had that idea?
JL: The one who came up with the idea for the cover picture was Flo, because he's really good with art; he studied in communications and marketing and stuff like that, and he came up with that and we looked at that and it all clicked right away. The cover is so brutal because when you think of what really happened to John the Baptist, it's so brutal -- how he died and for what he died. He died for a dance, the daughter danced and then he got his head chopped off, that's vile, it's "none so vile", because nobody these days would do a dance for somebody's head. Even though there is no blood and guts on the cover, it's classy, it looks good, but it's still very brutal. That's how we like to think of ourselves: we're really brutal but we try to do it in a good way, with good taste and originality. That cover took a lot of people by surprise."
Here's a small pic of the original