WÜRZBURG, Germany — Anas Modamani’s 2015 selfie with Chancellor Angela Merkel came to symbolize her decision to allow hundreds of thousands of unscreened migrants into Germany. But Mr. Modamani, a refugee from Syria, sought on Monday to prevent Facebook from allowing users to repost the image, or any altered version of it, after it repeatedly showed up in fake news reports linking him to terrorism.

The trial, one of several notable cases against Facebook in Germany, highlights several basic legal questions, such as who is responsible for content posted by anonymous sources and whether people who repost text they did not write, or an image that someone else altered, can be held responsible for defamation. Concern over nationalist and populist propaganda, as well as fake news, is growing in the country ahead of a general election scheduled for September.

The German justice minister, Heiko Maas, has suggested holding Facebook accountable for hate speech posted to its site, and a government-initiated task force that includes representatives from Facebook, Google and Twitter is examining how long it takes the companies to take down posts flagged as hateful. The panel is expected to report its findings in the coming months.

Who is Anas Modamani?

Mr. Modamani, now 19, fled Syria for Germany in 2015 and was living in a Berlin shelter when Ms. Merkel came to visit in September of that year.