The suit is seeking to compel Facebook to act faster - even pre-emptively - to remove such material, and thereby concede that the social network is also a media company and therefore liable for the content it publishes.
The lawsuit, which goes to court tomorrow, marks the latest attempt to hold Facebook more accountable for an upsurge in fake news. Germany, Europe's most populous nation, with cherished notions of personal privacy and a low tolerance for propaganda, has emerged as a particularly fierce battleground for the outlet.
"Facebook only deletes those URLs that are pointed out to them in written form," said Modamani's lawyer, Chan Jo Jun. "We are fighting for all reposts to be deleted."
As Facebook has come under fire for allowing the spread of fake news, the company has promised to take steps to combat the problem while maintaining that it is merely a platform for sharing information, not generating it.
The Europeans have been particularly aggressive. In May, the European Commission agreed on a new code of conduct with Facebook and other social-media platforms under which they would respond to reports of questionable content within 24 hours.
But nowhere in Europe has the pressure been stronger than in Germany - a country where the memory of Nazi propaganda and Cold War-era machinations have created a culture strongly adverse to hate speech and false reports. A proliferation of far-right and pro-Russian websites also have trained their sights on Merkel as she campaigns for re-election in a vote set for September, putting the issue of fake news front and centre in the public debate.
In response to calls for change, Facebook last month announced the start of a new effort in Germany in partnership with the nonprofit journalism network Correctiv. With the help of professional journalists, reports shared by users and identified as fake would be labeled as potentially suspect or false.
Yet the Germans may push Facebook to go even further. The country's Justice Ministry is monitoring how quickly Facebook, Twitter and YouTube delete potentially libelous fake news, reports inciting hate and other content considered illegal under domestic law. If the results show that Facebook has not made progress since a similar test in September, the German government has threatened to force it to comply.
"We're considering concrete legislative measures," said Justice Ministry spokesman Philip Scholz. He added, "We're also considering fines as a final option."
Modamani's lawyer has sought to sway German prosecutors to build a case against Facebook for years. Although prosecutors in Hamburg and Munich took a look at his claims that the network was allowing the spread of incendiary and hateful material, thus far they have failed to take action.
In the Modamani case, the suit is seeking to force Facebook not only to delete specific false or illegal posts reported by users, but also to adopt special filters that search the network and remove all other references to that content. Jun said that although Facebook claims to have deleted fake posts attacking his client, he found reposts of the images as recently as last week.
The claims centre largely around three images, which were widely spread and which Jun claims could still be circulating on Facebook. One shows the selfie of Modamani and Merkel next to security footage of a group of young men suspected of trying to set a homeless man on fire at a Berlin subway station on Christmas Eve. The face of one of the suspects is circled and falsely identified as Modamani.
"Merkel made selfie with one of the offenders in 2015!" it reads.
In another incident, a photo montage circulated on Facebook of Modamani with Merkel against the backdrop of a Berlin Christmas market following the December attack. The caption reads, "They are Merkel's dead."
An earlier claim had falsely linked Modamani to last year's Brussels attacks, alleging that Merkel "took a selfie with a terrorist". The image was initially posted by a user called "Anonymous" and, according to Jun, reposted at least 1000 times. Many times more users saw it.
"I love Facebook - I found an apartment through the network," Modamani told Spiegel Online last month. "But I also hate Facebook, because this Photoshop stuff simply never ceases."
In a statement, Facebook said that it had "already quickly disabled access to content" that Modamani's legal representatives had reported. "So we do not believe that legal action here is necessary or that it is the most effective way to resolve the situation."
