If you are using Imgur, just add the letter 'l' to the end of your link's random character string, right in front of the ".jpg" suffix, to change the display format of the picture from full-size to a large thumbnail as seen in the OP's last picture post; add the letter 'm' in the same spot to display the photo as a medium thumbnail as seen in the OP's second-to-last picture post.
If you right-click on those two images and select the 'view image' option you should see the URLs of the images to contain those two added letters right before the ".jpg" part.