When someone infringes your copyright, you have a limited time to make your claim. This is based on a legal principle called “statute of limitations.” Statutes of limitation, in general, are laws that prescribe the time limit to file lawsuits. The deadlines vary by the type of claim and maybe by the state where you live. The purpose of them is to reduce the unfairness of defending actions after a substantial period of time has elapsed. They allow people to go on with their lives, regardless of guilt, after a certain time.
Because copyrights are governed by federal law, there is only one statute of limitations for claims related to them. Copyright infringement claims have a three-year statute of limitations from the “last act” of the infringement. What constitutes the last act can vary. For example, if your image is published in a newspaper without your permission, you have three years from the date that the newspaper was distributed to file your claim in court. But if the infringement is continuing, such as when someone is using your image on the web without your consent, then the courts disagree whether the limitation period begins to run on a continuing wrong till the wrong is over and done with. It sometimes starts when you have “constructive” notice of the infringement, even if you don’t have actual knowledge of it.
Determining when a statute has started to run can get a bit tricky. If someone uses your photo without your permission, don’t sit on your claim. Note, however, to pursue any copyright infringement claims in court, you must first register your copyright with the U.S. Copyright Office.
Take my advice; get professional help.