Hi Fatihy,
Clicking on images in the blog post will show all images in any given post on a black background, with no text. The intent is to quickly show all the images as a sort of slide show.
When a writer uploads images, they can choose to show them in three sizes - small, medium or large. In the specific article you point out here the writer placed the images at various sizes just to give the post some variety.
The display size for blog post images is 880px wide. All images in any given post, with the exception of the title image at the top, are stored and shown at this width. Unfortunately, we typically don’t get images in large sizes to begin with.