This sounds no different than a bathing suit photo. I don't think you have to worry. It is not a good idea to give information and photos to people you meet on-line.
The above answer, and any follow up comments or emails is for informational purposes only and not meant as legal advice.
It's unlikely you will be prosecuted but you should learn from this mistake and stop sending pictures to strangers. If by chance someone from law enforcement does contact you regarding these pictures, you do not have to answer their questions. Inform your parents and have them hire an attorney for you.
I am a former Brooklyn Criminal Court Deputy Bureau Chief with over 17 years experience specializing in handling criminal cases. All answers are for information purposes only. Answering this question or any future questions does not form any attorney-client relationship. Be mindful, that answers are limited by the limited facts presented by the questioner and are not meant to take the place of competent legal advice by an attorney fully informed of all the facts surrounding your case. Also, be aware that nothing posted in a public forum such as this can be deemed confidential or privileged communication.
Semi nude means exactly what it says - partially nude. Usually that means exposure of genitals or exposure of breasts, but not both. This would be the US meaning. The United Kingdom has different standards on free speech from the United States, so I cannot speak to the truth of whether you could be found liable for sending such pics to a citizen of the UK.
However, in NY, the rule is that it would be illegal to send a picture of a minor engaged in a sexually explicit act (even if sent by the minor).
In general, under New York law it is a felony to:
•Knowingly use a minor in a sexually explicit performance.
•Promote material that contains a child under the age of 17 engaging in a sexually explicit act, or
•Possess material that contains a child under the age of 16 engaging in a sexual act.
If convicted, jail sentences could range from 2 to 15 years and will generally need to register as a sex offender.
However, a bra and panties shot might not pass as sexually explicit. It would depend upon the circumstances.
If you are a minor, and the UK person is not, I would suggest trying to keep the over-the-net pic sending G-rated or PG-rated. And remember, you never know what someone else might do with those images. Even if things are great now, if they turned sour, you could really regret sending those images.
When in doubt, don't send it out.
Best of luck.
This does not constitute legal advice or the engagement of my services as an attorney.