What sort of painting is it?
Art historians call this 'genre'.
Not too long ago, the various Art Academies (the Royal Academy in London, the Académie des Beaux-Arts in Paris, etc) decided not only what kinds of painting there were, but which were the more important.
In descending order they were:
History painting - any historical or mythological event
Portrait painting
Genre painting - confusingly titled: everyday life scenes
Landscape
Animal painting
Still life - arrangements of inanimate objects
Fashions change.
One might argue that portraiture is deemed to be more important in the 21st century.
There are other genres which are helpful:
Public art - art which is created for a public space, often having a civic function.
Religious art - art created to show or teach a religious truth or to inspire devotion.
(the jury is still out on whether there is such a genre as, say, Christian Art, or Islamic Art).
Propaganda or polemical art -
art designed to convince or persuade viewers, or to establish a view or attitude.
Obscene Art? Pornography?
Public and private tastes change all the time (as does the Law).
What might be considered obscene at one time, could be unremarkable at another. The nude human figure has long been a subject for art. Usually a (no doubt, fairly subjective) distinction is made between nudity and nakedness (where nudity = good), but history is full of occasions where images of the human body have been found unacceptable.
In recent years, a lot of work has been done on the different ways in which women's bodies and men's bodies have been portrayed and used in art. Whether these uses are appropriate or exploitation is a matter for discussion. A very specific subset of this debate has been about images of a naked Jesus on the Cross - historically and Biblically accurate, but ...
It is also true that some artists consider that their role includes a capacity to shock. This leaves us with an interesting conundrum: if the obscenity of the image is part of the artistic intention or project (if it is part of the artist's attempt to re-present the world to us), then surely it is art and ought to be displayed. Discuss!
Pornography is different. Pornography is created to arouse or excite sexual response. If that isn't the intention, then it isn't pornography.
This doesn't completely close the subject. Plenty of artists (amongst them JMW Turner) created pornographic images on commission. The most notorious case is possibly Gustave Courbet's Origine du monde (which won't be making an appearance on this website ...) Probably the most we can say, as people who care about art, is that these examples can still be considered for their artistic merit; they can certainly be evaluated in terms of the circumstances of their production and consumption. We don't need to insist that they should be on display in public spaces.