Expanding image toggles like the one on the right use a small "display version" of the image that the user can click on to display the full version. This can make your topic pages much easier to read because the larger versions of the image are only displayed when needed.
Help+Manual does all the work for you. You just select the full-size image you want to display and the smaller version is generated automatically.
Note that you can apply image styles to the image toggle preview to set a border and a standard width to an entire class of toggles.