It depends. It's a very fact specific analysis, and I can't give you a yes or no answer based on what you've posted. (Note: I'm not your lawyer, there is no client/lawyer relationship with you, the following is general advice that is not specific to your situation and may or may not be applicable.)
Generally speaking, it is not illegal to post a photo of someone on the internet without their permission if the person consented to the photo being taken or didn't have a reasonable expectation of privacy. I can stand in a public place, take pictures of anyone going by, and post them in private forums, public forums, or whatever kind of forum. There is no reasonable expectation of privacy in a public place.
If, on the other hand, the photo was taken in a private place, a locker room, a bathroom, etc., things could change. If the photo is being used for commercial purposes (AKA for profit), you might have options.
Internet privacy rights are in a state of flux. Federal rulings and state rulings by the various state court systems provide some guidance, but each situation is very fact specific. Without a great deal more information about the particulars in your situation, a meaning answer is not possible.
A good number of commentators suggest that the internet is a public forum with little privacy options available. Inroads to adopt and enforce privacy rights are being made, however.
A public picture of you taken in a public place and posted on the internet that causes no harm to you is quite different than an intimate picture of you taken in a private place that is posted publicly on the internet and causes you harm.
Contact a local lawyer that will provide a consultation to you so you might explain your situation in more detail.
Good luck to you.
NOTE: This answer is made available by the lawyer for educational purposes only. By using or participating in this site you understand that there is no attorney client privilege between you and the attorney responding. This site should not be used as a substitute for competent legal advice from a licensed professional attorney in your state. The law changes frequently and varies from jurisdiction to jurisdiction. The information and materials provided are general in nature, and may not apply to a specific factual or legal circumstance described in the question.