It is the biggest problem of blogger that it doesnot thumbnail but now i am giving you the solution of it.
Follow the steps to show any specfis thumbnail.
1.find any image hosting site like imgbb.2.upload your image there.
3.choose direct link and copy it. it is like as http://imgbb.1233.jpg or png.
4.copy the html code given below.
5.replace # with the direct link in code.
6.open your post from blogger and click on html.
7.at last of the post paste this code with your direct link.
8.now reopen your website and your see your upload image as thumbnail.
here it code given ;
