I was looking at jokes online and a pic of a lady with a slight piece of her lower body bikini area showing popped up. I quickly went to the next one, but went back for a split second to make sure I didn’t imagine it. Then when I verified it I looked away and went to the next one. Did I mortally sin? I never had the intention of looking at dirty pictures when I went on. I will not use that site ever again.
What were you thinking when you clicked back to look at it? Was it, “I know this is wrong, but that picture looked nice, and it felt good to look at it, so I’m going to look at it” and then proceeding to look at it and dwell on it and lust after her? That would make it a mortal sin, I think. But it doesn’t sound like you met these criteria, so it doesn’t sound like you committed a mortal sin.
Here’s a good guideline on sins of thought:
By your brief explanation,there is a potentiality of mortal sin,although one was not committed. Try to avoid even the occasions of sin.To deliberately place yourself in danger is a given prediction.I do not know what the disposition of your heart was and to be quite frank,it is no concern of mine.Your curiosity in future may very well land you in hot water.
Not to flee from the occasions of sin is to converse with the devil?By then,you will need no persuasion to consent.Sins of the flesh are notorious and many have,are and will fall to this vice of impurity.In a manner of speaking - no one is holier than David,stronger than Samson nor wiser than Solomon;yet,all fell to this very vice.
You must,so to speak,have some degree of respect for the devil,he is formidable and has existed through all the ages.Do not toy with him.He does not care how religious we are now,but will work to gain the ultimate end(our souls).He will wear us down temptation after temptation,sin by sin,bit by bit,day by day,year by year,even up until we lay dying.