WS here. I usually don't post in R, but I'm hoping maybe I can offer you some perspective from this side of the fence.
Obviously, I was the unfaithful one in our marriage, however before I met my wife (25 years ago) I was engaged to a girl who was very promiscuous and who cheated on me constantly. I remember the first time I asked her about what happened with the other man. She had told me that she was going out with her best girlfriend for the evening, but that plan works better when you tell your friend. Of course, the friend called and asked me where she was, and we got into the whole, "I thought she was with you" conversation. When she came home the next morning, I called her out on it, and asked for details.
She and the OM went to a local sports stadium, snuck in through a hole in the fence, and climbed high up into the bleachers. She gave me every detail... what they said, how it came around to them kissing, how he reached for her breasts, how she undid his pants... every - single - detail. And while I won't go into those here, I can tell you that I remember those details almost as if she had told me yesterday. She is long gone in my life and good riddance to her. Even though I don't care a bit about her, it still hurts to think about, because I was the one that was lied to and betrayed. The mental images have never left.
Now, on the other hand, when it comes to my own infidelity, there is almost nothing I remember with any detail in regard to intimacy. One of the more difficult conversations my wife and I had was when she asked me "who kissed who first?" and to this day, I honestly don't recall. There is nothing special I reminisce over, I don't long for her, I wouldn't even think of her if it weren't for the fact that I need to in order to do the work on myself and our marriage. I'm sure you've heard from other SI people that an affair is all about the WS, it is not about you. Nothing could be more true. And the truth is, the affair itself is the same. It wasn't about the OW. It was about me. She was just a means to an end, and while I did my best to try and convince myself that I "loved" her, I was no more capable of loving her than I was of loving my own wife or even myself. I was too selfish and needy. Everything I did with her was to make myself feel important and special and wanted. When I do think of the OW, I still think of her in terms of me, and what she brought to the table that I needed at that time. I did enough to give her back what she needed so that she'd keep feeding my ego. When she was gone from my life, it didn't take very long for her to be gone from my mind as well, because she never really mattered in the first place. I cried when she left, but I cried for me, not her, because I lost my toy, and got in trouble. I had all the emotional sincerity of a teenager, and I still struggle with that in some ways.
The reason I tell you all this is because I understand, as a man, how those images get burned into your brain. It is an invasion of privacy, in the emotional sense. It is as if that other man broke into your home, stole your wife, your life, your agency, and left you feeling violated and unsafe. It is like watching a car accident and yet being unable to look away. The things you imagine her doing, the things you imagine her feeling and thinking... are likely much worse than what really happened. Still, she handed over what was private and special between you and her, and gave it to some asshole without a second thought for you or the meaning behind what she was giving away, and that, more than anything, is likely what hurts the most. That she treated what was sacred to you, with no regard whatsoever. So if love and sex weren't of any value or meaning to her, then does that mean that you were meaningless to her? Pretty much.
Yeah, he might have the photos of her. You'll probably never know for sure. All I can tell you is that, whoever he is, he never cared about her, or you, or anyone but himself, and chances are very good that if he didn't get caught by his spouse, then he's likely hitting up some other woman to feed his ego. My point being, those photos matter a lot to you, but like all things in an affair, are probably meaningless to him, and while he may have pulled them out a few times (not to look at her really, rather, to try and boost his non-existent self value by remembering a time when he thought he was on top of the world) he will just move on to porn or his next infidelity partner. Remember, it is all about him, all the time, so if she's not in his life, then the photos really have no value. The value of nudes is not in having them, it is in getting them. When you aren't getting them, having them only reminds of that fact. In other words, the photos will hurt more than help now, at least, in the mind of a wayward.
I'm not sure if this helped you at all, but I hope maybe it did. Just remember that anything that happened during the affair was done by two (or more) emotionally stunted people who had the emotional capacity of a doorknob at the time. Absent some reason to change (such as trying to R with your spouse) they will likely remain the same. That guy thinks about your wife in the same way that he thinks about that great burger and fries he had for lunch, or how he felt when his favorite team beat their rivals. Those things were great and all, but not meaningful enough to hold on to in the long run.
Take care of yourself. Be kind to yourself, and give yourself permission to allow those thoughts and feelings to exist without having to give them power over you. Enough has already been taken from you without your permission. What you let go of, and hold on to, is yours alone to decide now. The memory of the photos has the power to hurt you because you value your wife and the marriage you thought you had, and what was yours and was special to you. So hold on to that, and don't allow anyone, not even yourself, to let them be a ball and chain that you drag behind you. I'm not saying to forgive or forget anyone or anything. It's like unplugging a lamp. Take away the power you give it, and it will have no power left to hurt you with.
((( bro hugs )))