A mortal sin requires 3 conditions to be present
from the Catechism:
1857 For a sin to be mortal, three conditions must together be met: "Mortal sin is sin whose object is grave matter and which is also committed with full knowledge and deliberate consent."131
- The act or omission must be Grave Matter
- the sinner must know the act or omission is Grave Matter
- The Act or omission must be freely consented to. (you cant be forced to comit a mortal sin by someone with a gun to your head… the sin is theirs not yours. Many things can impair the will, including Alcohol… where the sin is in getting drunk, the culpability for acts subsequently committed can be greatly lessened.)
Now. to come across a picture of a naked or topless woman is not always objectively grave matter. - Otherwise one could not morally enter many museums or some other public buildings where statues and pictures are present.
Even some of our churches have sacred art containing or consisting of pictures or statues of bare chested male and female figures.
Pornography is Grave matter. It is the deliberate formation of sexualised images or images of the sex act, which are then promoted for the sexual gratification of others.
A image of a topless woman, even if intended to be enticing to the viewer, is not Pornography as defined in the catechism.
it is Highly immodest, and it is definitely immoral to create, promote, or seek such images for lustful reasons.
But the situation you describe does not contain any of the 3 elements requred to be a Mortal Sin.
- The image described is not (from your description) automatically grave matter (it may have been, but it would not be good to give us sufficient detail to make that judgment). As a general rule I would say that to seek out deliberate photos of the “Page 3” variety are potentially “Grave matter”. but they are a whole different league from actual Pornography - which is an absolute, intrinsic evil.
- you did not deliberately seek this image. Nor did you intend any unchaste act (including deliberately entertaining unchaste thoughts). You gave no consent of will.
- It is clear that your knowledge of the morality of these matters is under developed. It is a moral obligation to properly form your conscience. I would advise you to read the appropriate parts of the Catechism.
Why not buy yourself a copy of YouCat?
Here’s a link on Amazon. but it’s avaialble from many places.
Its a catechism published by the Vatican which is designed to be easy to read and learn from, based on the far larger and more difficult to read Catechism of the Catholic Church.