#smilesfilm, a new iPhone app, is the digital manifestation of Ono's long-envisioned project. The app allows people around the world to view and upload snapshots of smiling faces.

It is also part of a global piece of her artwork, a changing collection of photos which reflect Ono's original vision of connecting people across the world.

"It is the simplest thing to make yourself healthy and make others feel good," the artist, peace activist and the widow of John Lennon, said about smiling.

The app features three sections -- dream, watch and smile. Users can look at recently uploaded snapshots geographically on a map, view them in a moving slideshow chronologically and take snapshots of their own smiling faces, which are collated into the app and placed on a map based on where the photo was taken.

Since June 1 more than 3,300 photos have been added to the app, which is also available online as a website.

#smilesfilm isn't the first time that Ono's artwork has featured the theme of smiling.

Her 1968 film No. 5, commonly known as SMILE, featured Lennon in the garden of his home in Weybridge, England, as he looked into the camera, shifting between a straight face and a full-on smile. The film premiered at the Chicago Film Festival in 1968.

Her 1971 piece "A Box of Smile" is a conceptual artwork, consisting of a small plastic box, which the viewer opens to reveal a mirror.

Ono admitted it is not always easy to smile.

"It was hard for me, too," she said in an email interview. "After my husband John Lennon passed away, I tried to smile for my health."

She suggested people just give it a try.

"Look at yourself in the mirror and force a smile. It is just awkward at first. But after you keep trying it every morning, one day you will start giving your smile to your whole body ... and then giving your smile to people with emotion."

The app, released last week, is available worldwide for iPhone. Photos can also be uploaded via Twitter and Instagram using the #smilesfilm hashtag.

The art project, which started as a Flickr group in 2009, originally consisted of a set of images of smiling faces collected at photo booths at art exhibits in Tokyo, Berlin and New Delhi.

It will be shown until September 9 at the Serpentine Gallery in London as part of the London 2012 Festival, where a photo booth will be available for visitors. Photos collected in the app will also be part of the exhibit.

(Editing by Patricia Reaney and Dale Hudson)

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