I realized that I need to shrink the image when I asked this question. I checked by clicking the edit. I could not find. How to shrink the image.
I don't think there is a button to shrink the image however, you can modify the url to use a smaller image for images hosted at imgur.com. Simply add a
m for medium or
s for small to the file name like so:
You can see more on the thumbnails available here
To enable better aspect ratios than that offered by Imgur's black magic offered in the previous answer, you could try using HTML tags like:
<img src="<image URL goes here>" width="<say 210>" height="<say 540>" alt="<alternate text in case the image does not display>" title="<some title text>"/>
I personally prefer this as the Imgur URL modifications mentioned above sometimes badly mess up aspect ratios of screenshots. This entails more effort than a modified link, but produces better results.