The illustration is an apotropaic mosaic from the entrance to the Domus di Giove Fulminatore in Ostia.
A prevailing theory of vision in antiquity was that the eyes were a source of rays or particles that probed the object of vision. Because of this, unwanted visual contact involved a sort of tactile violation, or even penetration (the "evil eye"). Even today we can talk about a "penetrating stare". Apotropaic images are an attempt to neutralize unwanted visual attacks by countering visual penetration with an image of equally potent penetration.
Mottos such as Hic Habitat Felicitas do not refer to any felicitas derived from sexual intercourse. Instead they should be seen as equivalent to whistling past a graveyard; an attempt to assert felicitas against any possible attack of evil.
Claudia Moser (Naked Power: The Phallus as an Apotropaic Symbol in the Images and Texts of Roman Italy, University of Pennsylvania ) cites Skinner (Sexuality in Greek and Roman Culture  ): “laughter is itself apotropaic” and “sexual imagery could be a source of mirth, releasing tension and anxiety.”
Take the lararium as emblematic of the profound difference of the cultus deorum from the Abrahamic religions. For cultores, the divine world is not a separate sphere. The gods participate in our community, our citizenship, our homes. We care for them (the meaning of cultor), and they care for us. Their fundamentally benevolent attitude towards us is shown in their gifts: agriculture, music and the arts, community life.
The lararium shows the democratic nature of the cultus deorum. Each pater- (or mater-) familias is at the same time the chief priest of the family cultus. The same pattern is seen today in Japan, with the household shrine (kamidana) and their family rituals, for example, on New Year Day. Removal of the lararium separates us from the gods and takes the care of our relationship with them out of our hands.