Zimmerman, who was acquitted last year of second-degree murder in Martin's death, auctioned off his first painting, a signed, 18-by-24-inch blue American flag featuring a part of the Pledge of Allegiance, on EBay for $100,099.99 last month.
Using the EBay account "therealgeorgez," Zimmerman explained why he had taken up art: "my art work allows me to reflect, providing a therapeutic outlet and allows me to remain indoors."
Zimmerman painted Corey in shades of red and orange holding her thumb and fingers together, with a quote on the top right of the frame that reads, "I have this much respect for the American judicial system."
Zimmerman's brother, Robert, first posted a photo of the painting on Twitter on Wednesday. He wrote that he was "very proud" of the artwork and announced it had received private offers on social media.
"Considering all options, incl. affordable prints," Robert Zimmerman wrote on Twitter.
AP said its photo of Corey, who is holding up her hand in the same position as in Zimmerman's painting, was from an April 2012 news conference in which the attorney announced Zimmerman would be charged with second-degree murder in the shooting death of Martin in Sanford, Fla.
The news agency said it sent a letter to Jayne Weintraub, one of Zimmerman's attorneys, asking that the sale of the painting "be blocked — and that, if there has been a sale, that the AP be paid damages."
On Friday, Zimmerman, who uses the Twitter handle "TherealGeorgeZ," wrote on his account: "No worries AP, I'll just take whatever U sue me for off your tab when I'm done suing you. Or ... I could put out how much U offered me 2."
AP spokesman Paul Colford said, "We don't know what he's talking about."
The news agency had a similar spat with artist Shepard Fairey over his use of an AP photo of then-Sen. Barack Obama for the artist's famous "HOPE" poster, which became popular during the 2008 presidential campaign. The legal dispute ended in 2011, when Fairey agreed to pay AP $1.6 million.