For example, I have a.jpg on the google drive.
-
Right click the image and click
Share... -
Click
Advancedand change theWho can accessoption toPublic on the web - Anyone on the Internet - Copy the
link to shareand you will have something like
https://drive.google.com/file/d/<FILE_ID>/view?usp=sharing
- Copy the <FILE_ID> to make a link like this:
https://drive.google.com/uc?export=view&id=<FILE_ID>
- Insert image in Markdown as ususal using the link from step 4.
For example:

Example: I have this octocat image in google, and its file id is 1913oZeBZPBNiUuk8gu3ZSbLBA2l_VQtG. You can try  in your markdown file or even in this answer.
Hope this helps.