I just recognized an edit from Treeston that brought up sth that others might like aswell.
Imgur has thumbnails for your image ready to use.
Assuming this is your default image:
The image id is: "ZPT6Cn0"
What you can do is add another character at the end directing to the thumbnail you want.
For now I found: "m", "s" and "t". I guess that referrs to medium, small and tiny?
ZPT6Cn0s - "s"
ZPT6Cn0t - "t"
ZPT6Cn0m - "m"
Thus thumbnail = IMAGEID+THUMBNAIL-IDENTIFIER