Sorry to butt in on a topic that is kind of delicate but I think an anonymous forum is actually a good place to learn about these things.
In confessing mortal sins, one must confess the number and type. The only reason you would have to be more specific than simply saying "pornography," would be if you watched pornography that contained sins that are distinct from the standard assumption of lust. Therefore, if you watched things that are against nature( lgbt stuff) or if for example the people involved were nuns or something(sacrilege), you should mention those details. It is not necessary to mention more than that, in fact you should not mention grisly details because of their disturbing nature, only that which is completely necessary to ascertain what kind of sin was committed.
I feel that's it's good to mention this here on the anonymous forum, because one could imagine a scenario in which a priest might not ask you to give these necessary clarifications for fear of him being accused of being a weirdo. Priests can't respond to accusations levelled against their conduct in the confessional, hence some reticence of their part.