A Bangladeshi man who distorted and posted photos of the prime minister has been sentenced to seven years in jail under tough internet laws that critics say are used to muzzle dissent.

Prime Minister Sheikh Hasina, re-elected in December in polls tainted by violence, mass arrests and claims of rigging, has been accused of increasing authoritarianism.

Mohammad Monir, 35, was found guilty late Wednesday by a Dhaka cyber tribunal for doctoring and publishing on social media images of Hasina and ex-president Zillur Rahman.

"He posted those distorted images in his Facebook status and made derogatory remarks in the photo captions," prosecutor Nazrul Islam Shamim told AFP.

He was convicted under Section 57 of the South Asian country's Information and Communication Technology (ICT) laws.

Shamim said that since the cyber court began functioning in 2013, at least seven people have been sentenced to jail for similar offences involving Hasina and others.

At least 200 more such cases are pending and in various stage of trial, he said.

Rights groups have documented how the ICT laws have been used to silence criticism in the country of 165 million people.

In recent months the ICT laws has been replaced by Digital Security Act, which critics say gives the authorities even wider powers to curb freedom of expression -- a charge rejected by the government.