I still remember this great movie from the 70s on St. Philip Neri…the devil comes as a woman to tempt him, and he smiles and says: “Do you think I am a young boy? The temptation is not
there (aiming his finger at her), it is
here! (touching his head)”.
Lust is the disordered enjoyment of sexual pleasure. It is grave matter and grounds for mortal sin. I can lust even by looking at a very modestly dressed woman!
Pornography relates specifically to the display of the sexual act. It is by all means not the only offense to lust, nor is it the only immoral thing to be avoided. There is much to be avoided in today’s world, and we ought to train ourselves in the discipline of self-mastery in order to achieve the balance of chastity and live our natural sexual drive in a healthy way.
It’s better to be away from what is immoral. Now, seeing something like that does not automatically become a sin

In fact, the sin is indulging in the thought or vision rather than rejecting it. The saints who lived ascetic lives and had no access to the Internet were tempted with visions of lustful things (now that’s harsh temptation) and they did not sin. This means the vision is not sinful if we did not seek to be exposed to it and if, having been exposed, we turn away, first inwardly, then outwardly.