Clickable text link on top of an image - PHP Site

Currently, the web site creates images on the fly, which contain varying text, depending on the page being viewed. Please see the example screen shot. In the screenshot you can see car registration/license plates images that have all been generated but the text is not selectable or clickable. At present it is the image as a whole that provides a hyperlink. THE TASK:- We would like for the text part of the image to be physically selectable and clickable as a link. These small yellow registration plate images are shown in the sites search results pages and on other browse pages. We need the solution applying wherever there is an instance of these small images. We have a development website set up for the work to be carried out. We require that the solution be provided on this development/test web site and instructions be provided for us to implement the change to the live web site ourselves.