This is the actual code WordPress generated for me when I just tried posting a picture. It refuses to post anything else besides a thumbnail for me. Notice how the width=”127″ tag comes after the URL. I put this after the height=”96″ and changed both values to the values that I resized my picture to using a photo editor. This solved the problem for me. I did this using the HTML Source Editor within the Write Post function.
You can also add a <center></center> tag within the paragraph tags in the code for the picture so it will be centered in the blog.