CONCORD, N.H. – A Dartmouth College professor was sentenced Monday to 5 1/2 years in prison after being caught with an extensive collection of child pornography — some of which he shared on the social media site Tumblr.

J. Martin Favor, on paid leave since his September arrest, pleaded guilty in March and resigned earlier this month. He could have received up to 10 years in prison. His lawyer said a decision hasn’t been made yet on whether Favor will appeal.

Favour will have to take part in sex offender treatment programs. His sentence, scheduled to start Aug. 5, will be followed by six years of supervised release.

U.S. Attorney Emily Gray Rice said “prosecuting those who possess child pornography is crucial to destabilizing this black market and undermining the normalization of child sexual abuse.”

Favour’s lawyer, George Ostler, said the Ivy League English professor recognized he suffers from an addiction and has committed himself to mental health treatment.

“Through the years, Mr. Favor played an active and a robust role in the academic community and was widely respected, not only at Dartmouth, but throughout the country,” Ostler said in a court document before sentencing.

Favour, 49, was arrested at his Plainfield home after authorities said he uploaded four suspected images of child porn through his account on Tumblr, a cross between a social networking site and a blog. Authorities say the images were uploaded to an account associated with his IP address and were traced back to him.

Prosecutors said investigators searching his home computer and flash drive found more than 500 videos and 300 still images depicting children, some as young as toddlers, being sexually abused.

Favour began teaching at Dartmouth in 1993 and was granted tenure six years later. He was an associate professor of English and former chairman of the African and African-American Studies program. Among his books are “Authentic Blackness: The Folk in the New Negro Renaissance.” Ostler said he was a mentor to many students.

In his sentencing recommendation, Assistant U.S. Attorney Nick Abramson said Favor, by his own admission, had been collecting child pornography for 15 years, “at least in part to satisfy the unnatural ‘urges’ upon which he swears he has not tangibly acted; urges from which he was able to abstain by avoiding regular interaction with young children.”

Abramson wrote that Favor’s “prolonged evasion of accountability for this criminal conduct was ultimately undone by his decision to distribute illicit images” through his Tumblr account.

Ostler wrote that his client “did not organize, catalogue or make all those images or videos available through any filing-sharing online community.” He said Favor viewed them privately and sought treatment soon after his arrest.

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Associated Press writer Michael Casey in Concord and researcher Rhonda Shafner in New York contributed to this report.