Check the "click-enlarge" checkbox in the back-end to allow users to click to show the full-size image.
With TYPO3, controlling the behavior of images is simple. Editors with no knowledge of HTML can easily manage links, popups, captions, alignment, and more.
Each image can be linked using the link field in the back-end. Multiple links can be added by separating each link with a comma. Values entered into the link field can be page id, a URL, or an e-mail address.