How do PS and cdr achieve the white background effect with rice husk on it?

First of all, the background is not white, but gray; Secondly, it is not like chaff, just some messy short lines.

The original picture should be a direct material picture, because there are repeated elements in it.

Of course, you can do it yourself. There are several ways.

One is to find a piece of paper like this. I remember this kind of paper, but it was colored. You can handle it a little after shooting. Of course, it is also possible to have this shading material online.

The second is to draw directly by yourself. In order to look more natural, I suggest you draw some small lines on the paper with a pencil, and then process them into brushes in PS after shooting, or download similar brushes from the Internet, and then open and adjust the relevant options in "Shape Dynamics" and "Scattering" in the brush settings to make the brushes scatter randomly. Then draw it on a gray background. Of course, it is best to use several brushes together, which looks more natural.