With some WordPress themes the /blog/ page which lists all posts shows grey view placeholder images instead of the the first image in the post.
This is caused by the blog post not having a “featured image” set.
To do this go to each blog post showing a grey image, edit that image, then in the bottom right hand side of the edit screen click the “featured image” link.
The media window will appear. Choose the image you want to use to replace the grey one on the blog list page. Click the “set featured image” button. The media window will disappear, and the image you chose will appear under the “featured image” heading.
Now click the Update button on the post, then revisit the /blog/ summary page. You should now see the grey image replaced by the image you set as the featured image.
Auto set featured image
The other option is to install a WordPress plugin that automatically chooses the first image in the post, and uses that as the featured image.
I hope this helps those of you who have this problem.