Custom Clickable Image
Whilst this mainly seems like a front-end development question, and Dr_Codswallop has perfectly summed up some steps in the comments to tackle that, as an answer for the Craft CMS specific side of the question there is a plugin I have used in the past that is very helpful, but it is only for Craft 2.x:

Donkeytail

I have had a look through the plugin store and I can't find an alternative plugin for Craft 3.x, so it looks like you will need to follow Dr_Codswallops instructions and build up something manually if you are running this version of Craft.