It’s not easy to be a songwriter in the pop world these days. Listeners rarely see your name. For anything but a giant hit, royalties from streaming are infinitesimal — and big tech companies seem to want to keep it that way.

And then there’s the shadow of “Blurred Lines.”

Four years after the copyright trial over that No. 1 song — in which Robin Thicke and Pharrell Williams, its primary writers, were ordered to pay more than $5 million for copying Marvin Gaye’s disco-era hit “Got to Give It Up” — the case still looms over the music industry and individual songwriters, who were left to wonder when homage bleeds into plagiarism.

Intellectual property lawyers and music executives interviewed for this article said the case had fueled a rise in copyright claims. In September, Ed Sheeran will go to court to defend “Thinking Out Loud,” a Grammy-winning song that has been accused of mimicking another Gaye classic, “Let’s Get It On.” Two years ago, Mr. Sheeran settled another suit by giving up part of his ownership in the Top 10 hit “Photograph,” which was accused of having similarities to “Amazing,” a song by the British singer-songwriter Matt Cardle.

The aftereffects of the “Blurred Lines” decision — which was upheld on appeal last year — have been felt most acutely by rank-and-file songwriters, who work in obscurity even as their creations propel others to stardom. The ramifications for them have been inescapable, affecting royalty splits, legal and insurance costs, and even how songs are composed.