A “Wizard of Oz” mural loomed over a D.C. park for 23 years. When other artists painted over it, one of the creators — a prominent street art curator — did something surprising: He sued.

For 23 years, a two-story mural in Northwest D.C. depicting the yellow-brick road, the Emerald City and the cast from “The Wizard of ... proponent of graffiti and mural art as historical and ...