The picture, posted on an aviation blog, was reportedly taken by a flight attendant to illustrate to airline managers the difficulty of dealing with passengers who cannot fit into seats.

It is unclear if the man was aware his picture was being taken or whether the flight, on US carrier American Airlines, took off with the passenger spilling out of his seat.

Airlines already offer extended seatbelts to larger passengers to comply with safety rules but a number of carriers now insist obese customers buy an extra seat.

US domestic no-frills airline Southwest has a “customer of size” policy that insists passengers who cannot lower both armrests buy a second ticket which is reimbursed if the flight is not full.

American Airlines does not have such a requirement but urges passengers to “recognize ahead of time that they may need to purchase two seats”.

The image, apparently taken on a Boeing 757, was sent to writer Kieran Daly and posted on his blog at aviation news website, Flightglobal.

It is not clear if the image has been altered but Mr Daly wrote: “This is sent to me with the absolute assurance that it's a genuine picture taken by a flight attendant at American Airlines. The F/A took it to show her manager what was happening on the aircraft (757???) and why she was unhappy about it. Seems the guy paid for only one seat and the gate staff let him board.”

Comments below the blog entry illustrate the debate over how to deal sensitively with obese passengers while ensuring others have enough room.

In a statement, American Airlines said: "At this time American Airlines is unable to confirm whether or not the image referred to was taken by a member of flight crew but will investigate the situation internally to determine if any of the airline's strict policies were not correctly applied.

"American Airlines’ primary concern is for the safety and comfort of its passengers and crews and consequently passengers are advised to book two seats if they are concerned that they will require them. If a flight is not full, however, passengers' needs would be accommodated without charge wherever possible."

I call BS. The two seats behind him are empty.

It is unclear if [...] the flight, on US carrier American Airlines, took off with the passenger spilling out of his seat.

Yes, but you can see that people are still boarding ahead of him. Those seats may have been assigned to other passengers already. They may have addressed this situation before take-off, but it's not clear that the seats behind him remained empty.

Per the article:

I think the quote from the article is the most salient point, considering planes usually embark the rear of the plane first, no?

He looks like he's about 7'6"

Or it's quite likely that there are kids in those two seats.