I've never sent one to anyone in particular, however I've posted many on some of the x-rated websites out there! Just for kicks. Some harmless anonymous fun!
I've posted a few on other sex forums and always enjoy the compliments; well who doesn't? I've also sent a handful of x-rated photos to people I've got really friendly with, which always gives me a thrill.
I sent a picture of my flaccid dick to a girl in Australia once, she was really excited about it and got lots of emails from her and how she would loved to be fucked by me.
Be careful as it can be considered a crime if you decide to do this as a prank to somebody. It's known as sexting.
If we have been texting for a while and got some idea about the person then I would send a picture. Sending a picture to a girl gives the conversation more interest