I don’t even know how to use imessage on my macbook
You either need Mountain Lion, or to download the beta for Lion. It just replaces iChat, and allows you to receive iMessages from iPhone/iPad/iPod touch users. No biggie.
Why would the person who received the picture show it to anyone else? I know whenever I got nudes, I’d keep those things…
Because it’s funny and some people are jerks like that. I’ve never shown nudes sent to me to my friends either, because hey those are for me.
However, I learned long ago that my senses of honesty and integrity are not the same as everyone else’s. The moral of the story: know who you’re sending nudes to, or just DGAF who sees them.