Adding links on images
Solution 1:
In Pages... It's grayed out because you do not have any text selected to become the link.
To place a link on a image, after you have added it to the page, insert a text box.
In the text box, type what you want to be the link, select it and press ⌘K to add the URL to the link.
Resize and reposition the text box over the image where you want it.
Here is an image with a link on it and clicked:
