Blog images in full page

Hi, I started writing on the blog of my site http://www.mariomassarotti.it
I added a new post and inserted an image. I would like to know if it is appropriate to respect a specific measure of the images or not.

At the bottom of the home page by clicking on the “go to blog” button, you will see the page with the chronology of the articles but without the image inserted. Why? Can you help me? Thank you