Rename files name

[aspfun]

There are about 200 photos' files in daily folders.
For example, in d:\20200910\ folder there are a lot of files like below.

IMG_1001.CR3
IMG_1002.CR3
...
IMG_1100.CR3

How to write a batch file to rename these files as below?

20200910_IMG_1001.CR3
20200910_IMG_1002.CR3
...
20200910_IMG_1100.CR3

Tomorow will rename as

20200911_IMG_1001.CR3
20200911_IMG_1002.CR3
...
20200911_IMG_1100.CR3