You can use what are called "image maps" in HTML.
To know more : https://en.wikipedia.org/wiki/Image_map

However, this technique is not recommended for 2 reasons:
- Some webmails interpret MAPS in a strange way. The coordinates being relative, they take as reference point the upper left corner of the web page instead of the upper left corner of the message! As a result, all the clickable parts are shifted...
- Some antispam products are sensitive to the presence of MAPS and will sanction the message by classifying it more easily as spam.

Another important note: to reduce the "spam score" it is recommended to balance the image / text ratio in your message.