Problem with the featured image (size)

Hi, I have a problem with my featured image. Theme used : NepalBuzz Here is my website : http://constitutiontime.com/ As you can see, there are 4 articles on the main page. The featured images have an equal size (3604 x 1205). But each time I want to add a featured image to my new articles, the image is bigger than the ones before. If you look at the first article that appears on the page, you will see that the size is not the same than the articles below. But the size of the image is the same. I didn't have this problem before. Can you help me please ?