Jurors - who heard testimony from Erbe and defendant Charles Nagel in the four-day trial in federal court in Brooklyn - deliberated less than a day before reaching a split verdict. They acquitted the Philadelphia resident on a separate stalking charge based on his attempts to meet her on location.
Nagel, 36, had described himself as an avid but mild-mannered autograph seeker and fan of "Criminal Intent." The USA network series featured Erbe as Detective Alexandra Eames for nine seasons.
When the forewoman announced the not-guilty portion of the verdict, Nagel responded with a joyful whimper. His demeanor quickly turned sullen when he learned of the conviction.
The defense had claimed that Nagel's daughter had posted the rude photos - one of Erbe's teenage daughter with an "I'm ugly" dialogue bubble - as a prank without his knowledge.
"I think (the jurors) had a hard time with those photos," defense attorney Robert Datner said afterward. Still, he added, the acquittal also showed they believed some of his client's behavior was "harmless and innocent."
Prosecutors had no immediate comment. There was no immediate response to a message left with Erbe's manager.
The government had claimed Nagel began harassing Erbe in 2008 by showing up at a Manhattan filming location with his wife and two daughters and trying to hug Erbe. She told the jury that after she fended him off, he kept staring at her as she completed her scene.
"I got a very bad feeling from him," said the 44-year-old actress.
Nagel, an aspiring songwriter who uses the name "Chaz Rose," later complained on a social network "that the victim had not responded to a song and letter he had written her, that this was causing him to become angry and that he knew where the program was filming," a criminal complaint says.
Nagel again went to a filming location in 2009 and approached Erbe, the complaint says. When she recognized him, she had a security guard tell him to leave.
In sometimes tearful testimony, Erbe said that Nagel persisted, writing her romantic letters - "I love you so much it hurts" - that left her even more shaken.
The actress recalled first seeing the photos and thinking "that I'm not going to let this go on anymore - that this is my daughter who is totally innocent and relatively defenseless."
Nagel described himself as being "shy" and "star-struck" in his encounters with the actress.
"She was sort of intimidating ... because she was in the character of Alexandra Eames and that was pretty cool," he said.