direct acces image url I searched but cannot find an answer to my question.

I'm using Drupal 7 and created content with image. The path of the content is http://example.com/page/content

My problem: I want to share the URL of the image to facebook.

http://example.com/sites/default/files/image01.jpg

But the request URL shows "404 not found".

I have set the media to show in public.

Did I miss something?
If that file does actually exist within /sites/default/files/ then your link should work.

Have you messed around with the .htaccess file in the root of your site? Or it could be the hosting package your on as there's a rule in that htaccess to not go into drupal if the file exists in that directory