founder Brandon Stanton used an open letter posted to his Facebook page to attack Donald Trump's campaign to be the Republican presidential nominee.
Stanton, and American photographer and blogger, said he had broken his own rule to stay away from politics because he came to realise "opposing you is no longer a political decision. It is a moral one."
"I’ve watched you retweet racist images," he wrote.
"I’ve watched you retweet racist lies. I’ve watched you take 48 hours to disavow white supremacy. I’ve watched you joyfully encourage violence, and promise to ‘pay the legal fees’ of those who commit violence on your behalf.
"I try my hardest not to be political. I’ve refused to interview several of your fellow candidates. I didn’t want to risk any personal goodwill by appearing to take sides in a contentious election."
Stanton originally interviewed ordinary New York residents and posted their stories in their own words on his Facebook page.
But as his work has become more popular his focus has shifted towards other countries, and in particular telling the stories of refugees.
"Over the last two years I have conducted extensive interviews with hundreds of Muslims, chosen at random, on the streets of Iran, Iraq, and Pakistan," Stanton wrote.
"I’ve also interviewed hundreds of Syrian and Iraqi refugees across seven different countries. And I can confirm— the hateful one is you.
Mr Trump, who is considered to be the frontrunner for the Republican presidential nomination, has refuted suggestions his rallies encourage violence, saying they were "lovefests".
However the billionaire businessman has reacted angrily to large groups of protesters who have interrupted recent rallies in Chicago and Ohio, including issuing threats to them and to other candidates.
In his letter, Stanton disputed Trump's repeated claims that he would unify the country.
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"You are not a ‘unifier’," he wrote.
"You are not ‘presidential.’ You are not a ‘victim’ of the very anger that you’ve joyfully enflamed for months.
"You are a man who has encouraged prejudice and violence in the pursuit of personal power. And though your words will no doubt change over the next few months, you will always remain who you are."
