What is the difference between linking to an image, a website, and an email address?

Answer 1

To link an image, use <img> tags. You need specify the image in quotes using the source attribute, src in the opening tag. For hyperlinking, the anchor tag, <a>, is used and the link is specified in the href attribute.
Text to be hyperlinked should be placed between the anchor tags.

Answer 2

If you mean linking with "href", linking a image and a website means the same: will redirect the user to the link when the click action is performed.
Linking a e-mail will start the default email software on the user's PC, like Outlook