India has launched its biggest ever survey to count its tiger population.
There has been a sharp decline in the number of tigers in India
The countrywide census focuses on national parks and reserves where scores of tigers have gone missing.
Wildlife experts have criticised the Indian government for failing to crack down on poachers and the illegal trade in tiger skins.
Around 3,500 tigers are left in India, compared with 40,000 a century ago. The new plan is the most ambitious yet to try to stem the decline, observers say.
The BBC's Navdhip Dhariwal in Panna National Park in central Madhya Pradesh state says the census will, for the first time, build a central portfolio of photographs and data of surviving cats to help monitor numbers.
The first stage of the survey involves checking the health of tiger habitats across 17 Indian states.
India is home to 40% of the world's tigers
There are 23 tiger reserves in India
An estimated 3,500 tigers are left in India
Tiger skins are prized for fashion and tiger bones for oriental medicines
Tiger pelts can fetch up to $12,500 in China
"It is [aimed at] estimating the population of tigers, getting what is the pre-condition of tigers in those areas, also estimating the habitat condition and quality," Qamar Qureshi of the Wildlife Institute in India, which is carrying out the survey, told the BBC.
Experts will go on to study the density of the surviving population.
At the Panna National Park, wardens already claim to have seen 34 tigers.
But conservationists warn there have been too few sightings and that figures may have been inflated to paint a rosy picture of how India's tigers are surviving.
Some say the new survey is a waste of time and money.
"To me the most important thing is protection and what we suffer from in India is a government which has reached an abysmal state where they're not able to protect our national parks and sanctuaries," says tiger expert Valmik Thapar.
"I believe this amount of energy should be spent in protection and only some sample surveys of estimation be done - because if you protect areas tigers flourish," he told the BBC.
The census was prompted after critics blamed the Indian government for failing to tackle poaching and an alarming rise in the trade of tiger carcasses.
Last year, it was discovered that almost all of the tiger population at the Sariska tiger reserve in Rajasthan, had been killed.
Our correspondent says the government wants to show it is now doing all it can to ensure the tigers' survival.
Wildlife campaigners, however, warn that it is already too late to guarantee their protection.