This is a genuine photograph. However, the size of the rat appears exaggerated in both the claim and the image. The large rodent was captured by an electrician in Hackney Downs in March 2016. When the snapshot first appeared, it was accompanied by the claim that the pictured animal was at least four feet (1.21 meters) long and weighed more than 25 pounds (over 11 kilograms). Neither of these dimensions came from a tape measure or scale, however; the estimates were given by the man who took the photograph:
Engineer Tony Smith discovered the animal's corpse, which he says weighed about 25lbs, while working on a block of flats in Hackney, east London.
He says that he found the monstrous creature lying in a busy next to a children's playground which backed onto a railway line near Hackney Downs.
Tony, 46, said: 'This is the largest rat I've ever seen in my entire life. 'I've got a cat and a Jack Russell and it was bigger than both of those put together. I'd say it was about four foot. 'We were going to stick it in the bin, but before we did we thought we better take a picture or people won't believe it's real.'
It appears that the more modern claim that this rat weighed twelve pounds comes from a conversion error. When experts in London weighed in on the size of this rat in 2016 (they mostly said that the claimed size was preposterous), they used kilograms instead of pounds. When this weight (almost 12 kg) was converted back to pounds, the number stayed the same.
But even this claim, which is less than half of the original estimate, appears to be widely overblown. The measurements are too big for London rats. The brown rat, which is commonly found in London, "only" grow to around a foot long:
"In our study that surveyed over a hundred brown rats from all over the UK, the maximum body length of fully-grown rodenticide 'super rats' was 26 cm (10.3 inches) with a tail length of 25 cm (9.8 inches)," says (Dougie Clarke from the University of Huddersfield, UK.) "So they are no different than what is expected for brown rats."
One of the biggest rats in the world — the Gambian pouched rat — can grow up to about three feet long. Other giant rats, such as New Guinea's woolly rats and the Northern Luzon giant cloud rat also get uncomfortably large, but fall well short of the claimed measurements.
That the London rat appears unusually monstrous may be a result of forced perspective, which can make an object appear much larger than it actually is since it is closer to the camera lens than the other objects in the image. The Hackney Council posted an example of forced perspective in order to quell fears that the neighborhood was experiencing an infestation of rodents of unusual size: