The Melbourne Marathon Festival has apologised after an image of a winning athlete posted to its Instagram page was apparently edited to obscure the logo of a competitor of its naming-rights sponsor.

The marathon, which attracted a record breaking 42,000 competitors on Sunday, is sponsored by major sporting brand Nike.

The festival shared images of race winners after the race, but it wasn't long before some social media users noticed something missing from an image of women's half-marathon winner Leanne Pompeani.

An image of Pompeani at first showed the long-distance runner without the Asics logo on her top.

Two images shared to celebrate four-time Olympian and women's marathon winner Genevieve Gregson were also taken from angles where the Puma logo on her top was not visible or obscured, including a shot taken from behind.

Comparatively, the Nike logo was visible on the image shared of male marathon winner Jack Rayner, who was wearing Nike clothing.

In a statement, the Melbourne Marathon Festival said the post had been made in error.

"These were subsequently removed and replaced as soon as management became aware. 

"We apologise to the affected parties and will be revising our internal processes to ensure this does not happen again."

In a statement Nike said it "did not direct changes or alterations to any images".

"We understand the image in question has since been corrected," a spokesperson said. 

Pompeani and Gregson declined to comment.

Adam Karg a professor of sports management at Deakin University said the use of edited images raised ethical questions.   

"If we're removing brands, what if we start adding brands as well?" he said.

He said augmented imagery is used in sports marketing to a degree, particularly on televised events where, for example, different brands relevant to the country the program is being viewed can appear.

"Virtual advertising, or changing the advertising behind people has always been something that we've become comfortable with.

"This as a new case is something we are not comfortable with," he said. 

Professor Karg said it also wasn't unusual for events and sponsors to use strategies where photographers were directed to capture images at certain angles so that competitor logos were less visible.

He referred to this as a "selective lens", but said actually editing brands out of images was not a mainstream practice. 

"When you're playing around with people's individual sponsors, as well as the social and ethical components of that, contractually, this is serving up a bit of a difficult space for athletes and managers of athletes," he said. 

Marketing expert Gary Mortimer said these types of incidents could often be the result of "overly cautious" decision-making rather than direction from sponsors.

He said a sponsoring company would typically want its branding along roads where the race is, on websites or on any press releases, but "reasonably wouldn't expect every participant to be wearing the branding".