Hiya - I'm a long-time lurker here and second-year applicant, though not in painting. I've considered a similar question, and the answer was really tricky for me. Firstly: I want to say that only you know the work and can make that decision. I'd ask you a couple things: if you include the photos and get rejected, will you question/fear that their inclusion was a determining factor? Likewise, if you don't include them and are rejected, will you question what would have happened had you been more bold? The answer to these questions might help you.
My gut tells me that it may not be the best idea to include these photos, especially for medium-specific programs. If the paintings themselves already make an appearance in the portfolio, you might not want to include a photograph with the same (albeit background) visual information. If an interdisciplinary practice is important to you, you might mention that in your statement and then add these photos to your interview portfolio (it's usually a good idea to bring new work to the interview). At the interview stage, you've already demonstrated your medium-specific skills/candidacy and the faculty have enough interest in you/your work that it may not be as big of a gamble at that point. Another point I'll make is that the inclusion of the photos might affect your performance/comfortability in the interview, especially considering they are nude. Do you think you could still speak as confidently, openly, and comfortably if they are included? If the answer is no, then it probably isn't worth the risk. Art history is steeped with nudes, so I could convince myself that it's totally professional and the faculty will be prepared to engage with that kind of work, but personally I'd feel a bit too bashful to include them in my own portfolio.
If these photos are stellar and you think they add enough interest, complexity, demonstration of skill, etc, and you would regret not including them, then go for it! I might suggest picking either the photo or the painting, but not both. I once tried to include a 3D object (from the portfolio) in a photograph (also intended for the portfolio) and received feedback that I should include one or the other. Of course that's only the advice from one of my mentors.
If all else fails, you can flip a coin to see how you're really feeling.