Question about tilemap and puting pictures in the gam

My unity version is 2019.4.4f1. When I drag a picture to the scene windows in unity and release it, if it is on the tilemap, then I get a material file in the root of the picture rather than put the picture in the game. Besides, when I delete the material file, the tilemap becomes purple.

This is a special drag and drop action when you drag a Texture (the picture) onto a GameObject with a Renderer (the Tilemap has a Tilemap Renderer). It creates a new material with the Texture and assigns it to the Renderer.

You may want to first drag your picture to the Hierarchy window and arrange its position from there?