Images can be linked to directly using either a link within the image, or as a text link as well.
Images are sometimes scaled down versions of themselves to fit into a specific space, or to make loading of the page faster. You may want to link directly to the full-size image instead so users can view all of the detail.
You have two options within a text block to link directly to an image.
First, you can create a link to the image itself when you place the image on a page or post. When you use the Add Media function and choose an image, in the Attachment Display Settings section you can click the drop down for Link To and choose Media File. This will create a link for when someone clicks on the image itself.
Once you make this choice, click Insert into page to place the image.
You can also link to the full size image using the text link option within the text block.