A critical blog post could land you in jail in communist Vietnam, but a satirical image of Cinderella which mocks the ruling elite? Likely to slip past the censors.

The country's roughly 33 million Internet users, armed only with laptops and a sense of humour, are driving broader social change in the authoritarian nation than scores of imprisoned firebrand bloggers, experts say.

From their calls for the health minister to resign -- a cause so popular that a state-run newspaper briefly took up the campaign -- to amusing attacks on ham-fisted censorship, Vietnam's ever-growing ranks of Internet users are finding their voice.

"The kids creating and sharing these images don't think of it as activism, for the most part. They're not necessarily campaigning for anything. They're just making jokes," said Patrick Sharbaugh, a digital culture researcher who has worked in Vietnam.

"An ersatz civil society is emerging out of this," he said.

Criticised over a spate of baby deaths after routine vaccinations, Health Minister Nguyen Thi Kim Tien was the target of hundreds of memes including unflattering photos of her with the words: "Without me, how would funeral services thrive".

In a one-party communist country where public loudspeaker systems still broadcast official news twice daily and all media are state-run, the space the Internet creates is important.

At the forefront of the revolution is the "meme" -- an idea or piece of content, similar to viral content, but changed or remixed as it spreads.

While still not as widely used in Vietnam as in the United States or China, "there's a lot of growth to come," said Ben Valentine, an American writer for The Civil Beat website which examines memes and viral media.

"It's very exciting," he added. "While censorship is extremely harmful socially, it can breed intense creativity."

- Cute Cat Theory -

It is difficult for Vietnam's government to stop the spread of memes.

Facebook is already is under a partial unofficial block that is easily circumvented by some 22 million Vietnamese who have accounts, and shutting it down totally risks upsetting, and even radicalising, otherwise content citizens.

This is an example of the Cute Cat Theory of Digital Activism, a term coined by academic Ethan Zuckerman in 2008.

Tools like Facebook -- used overwhelmingly to share "cute cat" pictures, baby photos or selfies -- can also be used for political content.

"Any tool that allows cute cat images to spread, is a tool that can allow activist messages to spread. So that is a challenge" for authoritarian regimes, said American artist and writer An Xiao Mina, who describes memes as the "street art of the Internet".

And under authoritarian regimes that use keyword search algorithms to delete messages, "the activist message becomes the cute cat," said Mina.

So to show support for dissident Chinese artist Ai Weiwei, whose name has been blocked on China's hugely popular Weibo microblogging site, people use photos of sunflower seeds -- a reference to one of his works.

- Change through laughter -

One of the most popular incubators of memes on the Vietnamese Internet is HaiVL -- the name means funny or hilarious in Vietnamese -- which opened two years ago and now gets 1.5 million visits a day.

The site censors openly political content and blocks repeat offenders, but much of the content touches on sensitive issues in society using humour.

"Everyone wants to be happy. I think HaiVL has helped many people to be happier by making them laugh more," said Vo Thanh Quang, co-founder and CEO of the company that runs the site.

The Tuyet Bitch Collective remixes Disney cartoons into satirical memes. In seven months they have acquired a quarter of a million followers on Facebook.

Another catalyst for change is the rise of viral videos, shot on smartphones, that have prompted mainstream media coverage and even jail terms in the case of two nursemaids caught abusing children.

"This is to me one of the most significant, cool things about the modern Internet in Vietnam... Hold to account abuses of power," said Anh-Minh Do, an editor at the Tech in Asia website.

When two policemen were caught on camera brawling in the street, the video went viral after it was set to Star Wars music with lightsabres digitally added.

"We can all laugh at police and laugh at the authorities. Because everybody knows about the corruption and stuff," he said. "Those kind of things are being brought into the light."