A US school is putting computer-linked cameras in its canteen to work out how many calories pupils get through at mealtimes.

They will photograph what foods children pile onto their trays and later capture what they do not finish eating.

Digital imaging analysis of the snapshots will then calculate how many calories each student ate.

Health officials in San Antonio Texas said the scheme, funded by a US Department of Agriculture grant, is the first of its kind in a US school, and will be so precise that the technology can identify a half-eaten pear left on a lunch tray.

Researchers hope parents will change eating habits at home once they see what their children are choosing in schools. The data also will be used to study what foods children are likely to choose and how much of if they are eating.

“This is very sophisticated,” said Roberto Trevino, director of the research centre which will oversee the programme.

Parents will be required to give consent for their children to participate, and receive regular reports showing what foods they are eating. Only the trays, and not children, will be photographed.

Pupils will be are assigned lunch trays with a unique bar code. After they fill their plates down the line, a camera above the cashier takes a picture of each tray.

When lunch is over and the children return their plates to the kitchen, another camera takes a snapshot of what is left. Software then analyses the before and after photos to calculate calories consumed and a report of nutrients in the foods.

Five elementary schools will take part. Researches selected poor, minority campuses where obesity rates and students at risk for diabetes are higher.