Outrage has erupted across the United States after a photo of two white police officers mounted on horseback walking a handcuffed black man by a rope – recalling the long history of violence, slavery and racism against African Americans during the era of segregation – went viral.

Vernon Hale, the police chief of the US city of Galveston in Texas state, issued an apology following the incident, but his statement drew more criticism for being “weak”.

Hale said the black man in the photo, Donald Neely, who was arrested on Saturday for trespassing, should have been taken to the station in a police car, instead of horse-mounted officers.

Neely was then escorted on foot, led by a length of rope and flanked by the two police.

“Although this is a trained technique and best practice in some scenarios, I believe our officers showed poor judgement in this instance,” said Hale, in a statement published on Monday on Facebook.

“First and foremost I must apologise to Mister Neely for this unnecessary embarrassment,” Hale said, adding that policy had been changed so that the technique would no longer be used.

Neely is free on bond. He has no listed telephone number and could not be reached for comment.

Hale toldThe Galveston County Daily Newsthat he regularly talks to his officers about how their actions affect people’s perception of the department.

“You have to be aware of the images we portray,” he said. “We talk about it when we talk about use of force, when we talk about vehicle pursuits. Quite frankly, I never would have dreamed of it in the context of mounted officers.”

‘Weak’ apology

But Hale’s statement sparked frustration, with some activist groups saying his response was “weak” and “inadequate”.

In an interview withAl Jazeera, Clayborne Carson of Stanford University said the incident was “not just a matter of training” the police officers.

“Anyone who has the slightest awareness of American history would understand the implication of seeing a black man paraded in that manner. It resonates with the worst aspects of racism, going back to slavery,” Carson said.

Others called for the officers to be penalised or fired for “humiliating” Neely in a manner that recalls extreme acts of racism from the country’s past, or even convicted criminals exhibited in public squares.

“This is 2019 and not 1819,” James Douglas, president of the NAACP's Houston chapter, told the Houston Chronicle.

Mary Patrick, president of the Galveston chapter of the NAACP, told theGalveston County Daily Newsthat the department had an obligation to explain the officers’ actions to the public. Patrick later said she had spoken with Hale and the police chief had the NAACP’s support.

Democratic 2020 hopeful Beto O’Rourke, who is from the West Texas city of El Paso, also denounced the incident, tweeting, “This moment demands accountability, justice, and honestly [sic] – because we need to call this out for what it is: racism at work.” (Al Jazeera and News Agencies)