I once made a confession and mentioned to the priest that I had seen some images on the internet with female nudity, but that I had not consented to any impurity. He considered it a mortal sin without making any further inquiries.

Some of us enjoy anonymous posting because we get to judge the idea of something not based on respect of persons but solely from the idea itself.

Does anyone know how to block specific website? I am unsure how to do this. If I can block 4chan it will stop be from going to it out of habit, the extra barrier should be enough to help.

I once made a confession and mentioned to the priest that I had seen some images on the internet with female nudity, but that I had not consented to any impurity. He considered it a mortal sin without making any further inquiries.

He said as an example that if a woman in a bikini pops up and I click on it, I am already commiting a mortal sin.

I discussed it no further and simply accepted what he as saying.

But I have read a lot of old, pre-council Moral Theology manuals, and they all say that immodesty is different from impurity. I mean, I can look at a nude woman and not commit a mortal sin, if it is not a proximate occasion of sin to me and if I don't consent to any impurity.

It is always a mortal sin to put yourself in a proximate occasion of sins of impurity, this much I know.

The issue is that there are degrees to remote and proximate occasions of sin, and it largely depends on the individual and the circuмstances.

My take is that the priest is being a rigorist, or is being overly simplistic because he probably thinks that I don't have a deep Moral Theology understanding.

It is obviously better not to look at nude people, but I think that it is important to be able to differ mortal and venial sin.

This is annonymous because I think that it is inappropriate to disclose our confessions.

I would appreciate comments and discussion from people who have a deeper knowledge of Moral Theology.

The example the priest gave you illustrates what he understood about your situation:

"He said as an example that if a woman in a bikini pops up and I click on it, I am already committing a mortal sin."

Taken on its own, I would consider this venial. 

But is it possible that this priest's response was due to knowing the other sins committed and confessed at the time?  Or is this sin supposed to be taken by itself?  In other words, can something like this (clicking on a sexy image, taking the bait as it were) be more than a venial sin for someone who has a tendency to mortally sin otherwise? 

It seems to me that we should give the priest the benefit of the doubt as we don't know all that happened in the confessional.

Perhaps, but we don't know the priest's name, and there's no harm in discussing the question based on the parameters laid out by the OP.  There are priests out there who are not properly trained in moral theology, and some who impose some of their own scrupulous attitudes (there are priest, too, who suffer from scruples) onto the consciences of others.

I'd like to at least know which group this priest belongs to, because it could cast aspersions on the quality of the seminary training there.

Why would someone confess something that they already believe to not be a sin?