The protest - with the message "Islam is part of Germany?" written in yellow chalk on the pavement -- bore the logo of the far-right Identitarian Movement, which is under surveillance by Germany's domestic security service.
The pictures, candles and red roses were put there Thursday, hours after a German court jailed for life Hussein Khavari, an asylum seeker claiming to be from Afghanistan, for the 2016 rape and murder of a medical student.
An image of his victim, Maria Ladenburger, 19, was among those of four young women placed in picture frames on the pavement, together with 14 candles and the flowers, outside Merkel's office in the Baltic Sea town of Stralsund.
Merkel has faced a harsh backlash against her decision in 2015 to open German borders to a mass influx of mostly Muslim asylum seekers.
It has sparked the rise of the anti-immigration Alternative for Germany (AfD) party, the anti-Islam Pegida street movement, and the white pride Identitarian Movement.
Merkel this week further angered the extreme right by reiterating that, although Germany is historically mainly shaped by its Christian-Judaic tradition, today, with four million Muslims in the country, "Islam has become part of Germany".
Police told AFP they had removed the objects and were investigating whether a criminal offence had been committed.
The other photos were marked with the names Mia, Mireille and Keira.
A girl publicly identified only as Mia, 15, from the town of Kandel was stabbed to death in December in a supermarket by her former boyfriend, a refugee from Afghanistan believed to be around 20 years old.
Mireille, 17, was stabbed to death in March in Flensburg, and police have arrested as the chief suspect an 18-year-old Afghan asylum seeker.
And Keira, 14, was killed in a knife attack in early March in Berlin.
Initially false reports spread online pointing to an Afghan attacker, before a 15-year-old German fellow student confessed to the killing, police said.