The photograph of Tomlinson was submitted to Demotix by contributor Anna M. Weaver and sold to the Guardian, which subscribes to the site's daily features email and feed of images.
Content from the site is made available on an exclusive and non-exclusive basis with 50 per cent of any fee charged given to the photographer or filmmaker.
Demotix images have previously been used by the Telegraph, but this is the site's first front page, Turi Munthe, CEO and founder of Demotix, told Journalism.co.uk.
"It is absolutely no surprise that our first real coup, as a street journalist wire service, should be a picture that represents a people-versus-state story," said Munthe.
"The story of Ian Tomlinson's death is absolutely tragic, abominable, and symbolic of so much worse besides, but this image on the front page of the Guardian shows how vitally important street journalists are - for truth telling everywhere. It's what street journalism does best. It's the weapon of the little guy."
Demotix has proved this model can work in the UK, but now it must make it work on a global level, he added.
More country-based features are currently being developed on the site to help its network of contributors increase their coverage of local news.