According to the Imgur API documentation the s
suffix actually means "small square" not
"small thumbnail". This means the image is cropped to fit into a small square. You probably want
to use the t
suffix which only resizes the image.
Here's the complete documentation on suffixes:
There are 6 total thumbnails that an image can be resized to. Each one is accessable by
appending a single character suffix to the end of the image id, and before the file extension.
The thumbnails are:
Thumbnail Suffix Thumbnail Name Thumbnail Size Keeps Image Proportions
s Small Square 90x90 No
b Big Square 160x160 No
t Small Thumbnail 160x160 Yes
m Medium Thumbnail 320x320 Yes
l Large Thumbnail 640x640 Yes
h Huge Thumbnail 1024x1024 Yes
For example, the image located at http://i.imgur.com/12345.jpg
has
the Medium Thumbnail located at http://i.imgur.com/12345m.jpg
Here's what your second sample image looks like using the s
, t
and m
suffixes:

If you want a different size than one of those listed above you can also use HTML directly in your post. For example if you wanted a really small thumbnail you could use this:
<img src="http://i.stack.imgur.com/vaKUB.jpg" height="20" />
To get this:

While this later method isn't as easy as just adding a suffix to the URL, it does have the advantage that people can view the full size image (as uploaded to Imgur) by right clicking on the thumbnail image.