The 30-year-old was sent home from Celtic's training base in Wales last week while allegations of improper online behaviour were investigated. It is understood the allegations surrounded claims he sent private online messages to an underage girl.
Officers have now been alerted to a second image linked to a teenager following a report in the Daily Record newspaper.
A spokeswoman for Police Scotland said: "We are aware of the social media content and the matter is currently being assessed."
The validity of the second image has not been confirmed, but according to the Daily Record, it has been circulated across social media, and appears to show Griffiths responding to a second teenager asking for a picture.
Griffiths, who joined Celtic from from Wolverhampton Wanderers in 2014, this month signed a new one-year contract extension with the Scottish Premiership club.
The striker, who has been capped 22 times by Scotland, had not been a regular starter under former manager, Neil Lennon, then caretaker manager, John Kennedy, throughout last season.
He had been criticised by Lennon for his physical condition on his return after lockdown.
Griffiths was also left out of the Scotland squad by national men’s team manager Steve Clarke for the Euro 2020 finals.
Earlier in the week, Celtic said that it had been made aware of online comments concerning Griffiths, and that the club would look at the matter “carefully.”