The answer is this, and the two PNG images in the middle are just too big. i dunno the syntax for how to do this and i only am copying syntax from other answers.
When you upload images using the "add images" button, the images get copied to Imgur, and multiple resolution copies are made in addition to the original. By default, the original is selected. However, you can easily change which one is used by appending a modifier to the link. For a visual example, consider the following image from your post:
The link for that picture is http://i.stack.imgur.com/RbokL.png. Now the resized copies must be different links, so they are creatively named RbokLs.png, RbokLm.png, and RbokLl.png. Note that I am taking the existing hashed base file name (RbokL) and adding either s, m, or l for the small, medium, or large version.
Keep in mind that you need to upload them to the Imgur service for this to work (that's what the add picture button does). Your post just links to the wikimedia pictures, which is plagiarism (no attribution) and will break if they ever change the link. Please fix that.