On this page (link below), if you put your mouse over the image and right-click,
mouse down to "properties" ... The file type shows Type: JPEG image
But on your main page, the same image shows: Type: text/html
So it might be how you created the entry. When you entered it, did you
use the text editor box (insert image)? Or did you just type in an image name?
This is a tough one to answer without seeing you operate your WP admin panel.