So bad it's good: Why do people love these terrible paintings?

Last year Laura was browsing in a charity shop in Devon when two pictures caught her eye.

An admirer of kitsch art, she took a quick snap of two paintings – a portrait of a man who looked like a cross between Rasputin and Osama Bin Laden, and a ghostly Viking head floating above a seascape – with her phone and shared it on Facebook.

The picture proved to be very popular among her friends. One of them, Becky, suggested she start a group to share such finds and Terrible Art in Charity Shops was born. It's grown rapidly in popularity, with an overall membership in excess of 20,000, and a hardcore of posters who actively hunt for pictures to share.

Laura – who asked BBC Arts not to disclose her surname – revealed some charity shops are actively promoting the group.

She said: "We've had members who found out about our page through the charity shops themselves. And more often than not they buy the art themselves, so we hope the charities are benefiting not just from increased footfall but also in sales."

In some ways, the popularity of group is difficult to fathom. Why spend time looking at paintings that are, by definition, not very good?

Humour is part of the appeal, according to Laura.

She said: "This might be the only place on the internet where people write ROFL [Rolling On the Floor Laughing] in their posts and I believe them."

But they're not just having a laugh at the expense of paintings which haven't turned out well.

Laura added: "It can also be very appealing emotionally – something about the wonkiness can be very endearing.

"We have a lot of artists and teachers within our membership and I think the freedom to be permitted to be openly honest and make fun of the work that is posted is a liberating experience.

"In a country famed for being overly polite it is a liberating experience to say what you really think."

As well as Laura and Becky, there are eight other volunteers who give up their time to administrate the group and moderate the comments.

Laura said: "Our team deletes anything too near the knuckle, anything personal, and any posts which don't include 'art' in order to keep our feed clutter-free and full of terribleness!

"We believe we have firm but fair rules. Increasingly the members themselves moderate the group and they soon see off anything inappropriate."

One thing they don't do, however, is define what terrible art actually is.

Laura said: "'Terrible to us could mean the subject matter, the execution, the type or condition of painting - we've even had a pop at a few Old Masters in our time.

"There are some art experts in the group, and some very talented artists: but the one thing we all agree on is that art is subjective and everything is fair game for a gentle mocking.

"For that reason we do not restrict posts based on the quality of the work or whether or not they are 'bad'. This has often caused debate on some threads where an artwork from a particularly well known artist has been posted but that just goes to prove that this group can also be an educational experience."

But Laura, Becky and co are not the only group of friends celebrating bad art. On the other side of the Atlantic there's a organisation who've been at it for nearly a quarter of a century.

Bad art is like pornography, according to Michael Frank, the Museum of Bad Art's (MOBA) Curator-in-Chief. He said: "While I find it difficult to articulately define it, I know it when I see it."

Louise Sacco, MOBA's Permanent Acting Interim Executive Director, told BBC Arts that the museum has stringent bad art criteria.

She said: "First, it must be art. To us, that means it is sincere and original and the artist has something to communicate. Second, something must have gone wrong in a way that results in a compelling image. Boring works don’t make it at MOBA."

MOBA's story began when Scott Wilson found a painting of an elderly woman in a bin. His friend Jerry Reilly thought it was 'so bad, it’s good' and hung the piece, which they called Lucy in the Field With Flowers, in his home.

Friends began to donate other 'bad' pieces to Reilly and he, along his wife, decided to throw a party in celebration, dubbing it the opening of the Museum of Bad Art. The party was such a success that they decided bad art deserved a larger audience.

MOBA's collection has now grown to contain over 800 pieces. It has had a number of physical homes, and while they maintain a small exhibition in the Somerville Theatre near Boston, Massachusetts, their audience is now primarily an online one.

Sacco said: "We were early users of the internet with a regular e-letter by 1995 and a website soon after. These days, our strongest presence is on Facebook. We post new acquisitions, explain what we see in them and let the conversations unwind."

In general, artists do not object to being part of the MOBA collection. Sacco said: "Only twice, out of 800 pieces, an artist has contacted us, unhappy that we have their work.

"In both cases, the pieces had been rescued from the public refuse system. Since we have no interest in insulting artists or making them unhappy, we offered to return the work or destroy it. Both artists asked us to destroy it, which we did, very sadly."

People are also happy to be connected to MOBA, including the family who owned the painting which started it all, Lucy in the Field With Flowers.

Sacco said: "A woman called to tell us that it was a picture of her grandmother. Nana lived with an aunt. When Nana died, Auntie was bereft. The nieces and nephews got together and commissioned a painting of Nana, from two photos.

"When it was unveiled, the nieces and nephews were appalled, but Auntie was thrilled and proudly hung it in her house. When Auntie died and the house was cleared, the painting was thrown in the trash.

"In the two photos supplied to the artist, Nana was sitting in one and standing in the other photo. That explains the odd pose. They told the artist that Nana's favourite colour was blue so they would like to see her in a blue dress. The artist said the sky was yellow because you couldn't put a blue sky behind a blue dress!

"The family was thrilled that we were celebrating this work. It was on the cover of our first book. This family bought dozens of copies."

Why does Sacco think viewers are attracted to bad art?

She said: "These are works that raise questions, invite conversation, and are remembered. We never say anything negative about the art or the artists, beyond the name of our institution. We love the works and we celebrate the artists."

Sacco's personal favourite is Sunday on The Pot With George.

MOBA use the following description for the painting: "Can the swirling steam melt away the huge weight of George’s corporate responsibilities? This pointillist [where countless tiny dots of pure colour are used] piece is curious for meticulous attention to fine detail, such as the stitching around the edge of the towel, in contrast to the almost careless disregard for the subject’s feet."

Sacco summarises it slightly differently: "I love this because it always gets me thinking about how much skill, time, and planning pointillism requires.

"Why would Mr Gedraitis use his obvious talent to portray this guy in his tighty whities?"