Walmart is having to defend itself after a photo showed a sign reading “Own The School Year Like A Hero” purportedly atop a gun-filled case in one of its stores.

A Twitter user told the Washington Post she recently took a photo of the sign, apparently one that’s used in Walmart’s current superhero-themed “back to school” marketing campaign, at a company store in Evansville, Indiana. The image quickly drew criticism on social media, with some people expressing outrage and citing school shootings.

After word of the photograph spread, Walmart apologized and said over Twitter than the sign had been removed.

But Walmart spokesman Charles Crowson told CBS News on Thursday that a company investigation, including a review of surveillance footage, found that the photo was not taken at the store. The retail giant also concluded the sign did not appear at its only other Evansville store that sells firearms.

“We have looked at videos and photographs of the sporting department, and there was no indication of the sign being there,” Crowson said.

“The Evansville store doesn’t even have those gun displays,” he said, adding that such a display “would never be acceptable” in the company’s stores.

Crowson said Walmart is still trying to determine the origin of the photo. While not ruling out that an employee may have posted the sign, he said it could have been a customer prank or the photograph may have been digitally manipulated.