A few observations:
I think you're worrying about something that has increasingly little impact in the world. There are so many nude pictures of so many people out there that it's becoming unusual for young people not to have at least one nude pic floating around the internet. You're not in a field where conservative Judeo-Christian personal values are necessary so I wouldn't worry about it at all. I tend to think that as people trend to putting nude pics of themselves out on the internet that Americans might finally begin to loosen their ridiculous obsession with nudity.
I also think that anyone who has seen your nude pics won't give a damn. Think of the venues where you might post them and then consider that for someone to admit they've seen your nudes, they have to admit they were looking for them. Your pics aren't going to just pop-up on CNN's homepage one morning. If someone says they've seen you nude, well then take it as a compliment and maybe even a come-on. If someone has the nerve to circulate your nudes around the office, that is fertile ground for a sexual harassment suit.
Regardless of what you look like, think about what Thadjock said. You're a man, you've got genitals. Of course you have a penis and testicles; those are what make you a man and gender is one of the few things the English language is very insistent upon. The very first thing someone does when they meet or talk to someone else is determine what sex that person is. It's not as though people don't know what you have under your trousers so what difference does it make? Muriel in accounting saw your penis! Horrors! BFD, Earl, BFD. Anyone who would purposely try to embarrass you is an asshole and the onus is upon that person. You can't be embarrassed unless you allow yourself to be.
I've run into one guy online who worked where I did at Time Warner who had nudes posted. I didn't know who he was until we chatted. The guy is really hung, nice, and has nothing to be embarrassed about. It didn't occur to me to circulate his nudes at work because it's no big deal to me and it had nothing to do with work. I suspect that's the case with most people.
No matter who you are or what you look like, there you are and whether people you know see you nude or not, it's ultimately not a big deal. We're all nude underneath clothing and like I said, what else did they expect to find?
Personally, I think you have absolutely nothing to be embarrassed about. Anyone who knows you well enough as coworker might knows the kind of man you are and wouldn't do these things to you. It takes a real sociopath to want to hurt a good person.