The image of 49-year-old Janice Morris cowering on a park bench in Bury St Edmunds, Suffolk, prompted public outrage after it was shared across the internet.
Five teenage boys admitted their part in the incident at an earlier hearing, but a sixth boy denied a public offence and forced Ms Morris to give evidence at an earlier trial.
Ms Morris told the trial that the incident left her feeling ‘a bit shell-shocked, a bit raw’.
The boy was found guilty of a public order offence and was sentenced at Ipswich Magistrates’ Court on Thursday to a reparation order.
The order requires the 17-year-old to complete 24 hours of work, through the youth service, over a three-month period.
He was also ordered to pay Ms Morris £150 compensation and £640 in court costs.
Lead magistrate David Broughton told the boy: ‘We have recognised your remorse.’
The earlier trial heard the boy was one of four who posed in the photograph which was shared online in July 2018.
He had denied a public order offence, stating Ms Morris was already covered in flour before he arrived, but was convicted as magistrate Sally Westwood said the photo ‘clearly indicates (the defendant) as a member of the group’.
She added: ‘He was not a bystander, he was smiling, pointing at Ms Morris.’
Magistrates were told that Ms Morris is schizophrenic and alcohol-dependent.
The defendant, who sat beside his father in court, told the earlier hearing he went to the police station voluntarily after he saw the photo on Facebook.
At his sentencing hearing, he told magistrates: ‘I just feel like I’ve matured a lot and I won’t be back here again.’
The court heard he attends college, has an evening job and goes to the gym three times per week.
Asked if things had changed since the incident, the boy said: ‘My parents ask where I’m going more, and what I’m doing to make sure I’m not with the same people I was with.’
His father told the hearing: ‘Things changed a lot. We talk more, we’re more controlling, he’s changed friends, he’s completely different.’
The boy told magistrates he would pay the money owed to the court himself.
Four male youth defendants and 18-year-old Cohan Semple, of Bury St Edmunds, admitted a public order offence at an earlier hearing and were sentenced last year.
The four youths – a 17-year-old, a 16-year-old and two 15-year-olds – were sentenced to referral orders and Semple, who posted the photograph on his Snapchat before it was shared more widely by others, was sentenced to a year-long community order.