Too large photos

My latest posts literally display a nasty shortcoming. When I upload an image, it doesn’t appear on my post as a compact and clickable middle-sized thumbnail. Instead, the image presents itself in the original size, taking a considerable part of my post’s space. It almost dwarfs my text. This looks ugly.

I have tried to change my theme, but the problem persists.

The page I need help with: [log in to see the link]