Online outrage is being directed at Wal-Mart for a gun display at one of its stores, after a photo went viral on Wednesday of a sign that hung above it.

The photo shows a back-to-school banner that reads "Own the school year like a hero" situated above a glass case full of guns.

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"What's seen in this photograph would never be acceptable in our stores," a Wal-Mart spokesperson told CNBC in a statement. "We regret this situation and are looking into how it could have happened."

Initial reports said the store was in Evansville, Indiana, but that has not been confirmed by Wal-Mart as of Thursday afternoon. The company had started its investigation midday Wednesday, after the photo began circulating.

The customer who initially tweeted the photo and who also spoke with The Washington Post has since taken her Twitter account private.

The woman, Leeanna May, insisted in an interview with the Post that the photo was taken in Evansville.

"We have already lost so many innocent lives to guns," May told the Post. "People don't seem to honestly care."

But Wal-Mart's latest tweets to unhappy customers tell a different story. It appears there is still some confusion regarding which store displayed the sign.

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After initially tweeting about removing the sign in Evansville, Wal-Mart is now looking into whether the photo was doctored or if the display of guns was part of a prank by customers.

This isn't the first time Wal-Mart has come under a viral attack for its products.

In July, Wal-Mart used a racist term to describe a wig cap sold on its website by a third party. The color of the hat was listed as "n—– brown."

The retailer also drew fire in 2016, prior to Sept. 11, when a store used Coca-Cola products to build two towers signifying the World Trade Center. A banner reading "We will never forget" hung above it.

— CNBC's Courtney Reagan contributed to this reporting.