The image singling out the suspect does not clearly show the face, and police, who released the photographs on YouTube, asked for the public's help in identifying and finding the person.
Ten men, seven women and a girl and a boy, both 10 years old, were hit when one or more people opened fire at the parade on Sunday. Police had earlier said they were looking for three suspects, adding that a motive for the shooting was unknown.
The photographs first show crowds of people in a street, and then the crowd is seen scattering and ducking. The final image focuses on what appears to be a man in a white shirt leaving the scene on foot as other people are lying on the pavement. The image does not clearly show his face.
A police spokesman said on Monday the investigation was continuing.
Two victims underwent surgery and the children were grazed but in good condition, police said. It was unclear if the victims were marching or watching the parade.
Police Superintendent Ronal Serpas has said a witness reported hearing two different types of gunshots, indicating two weapons were involved.
Violent crime in New Orleans ranks above the national average in FBI surveys. A poll of residents in 2010 found crime to be their greatest concern.
(Reporting by Corrie MacLaggan; Editing by Gary Hill)