Can a neighbor be sued if they put a photo of me online as a sex offender if it was never true

Defamation is the publication (communication to a person other than yourself) of information about you that is untrue.  The defense against defamation is that the information is true.  Thus if the information was posted online (publication) and the information is not true, the neighbor could be sued.  However, one issue with civil cases concerns damages.  What injuries have you had concerning this false publication?  If you haven't had any damages, then an attorney is unlikely to pursue the case even if defamation occurred.  This is because the neighbor might be found to have defamed you, but you may not be awarded any damages.  You would need to be able to prove your damages in court.  You need to contact a local attorney to discuss this prior to taking action. What may be better in your case is to contact local counsel and ask them to draft a letter telling the neighbor to stop or they may be sued.