Depends on the girl. Honestly your best bet is to send one to a girl you're dating while y'all are sexting or something,much less risky and rude that way.
NEVER SEND UNSOLICITED DICK PICS. I don't know, some girls may be into dick pics? In general, I don't think penises are attractive genitals. I may be biased, though, being a lesbian.
Have some class. Use a banana.
Might as well roll with it because you accidentally sent her the blackmail and it would seem that she was impressed.
At least that's what the romantic comedy/tragedy writer part of my brain is gonna run with.
*sobs uncontrollably
Well... simple really. I'm firing you so I can fuck you.