It is just about the worst betrayal you can do in an online way. The only thing worst would be if they posted name address and phone number along with it.
Some people are just... mean
You have to be VERY careful who you give pictures of that sort too, and you might as well understand that it is most likely they will get on the internet...
The person I gave mine too didn't betray me, but she had a jealous sister who found the pics, and the rest is history. So even if the person is trustworthy, you have to be concerned at who else has access to their stuff