How to use an image as an INVISIBLE button in Ionic?

I need to use a predesigned image composed of 5 different images as a button. I tried to use 5 invisible buttons on top of the images but they loose their position when testing on a device. So I'm obligated to use the actual image as the button.

What I did was to put the 5 individual images on top of the big composed image (they don't quite match), and make them invisible with visibility: hidden and adding a ng-click function so they are buttons. The problem is the ng-click doesn't work while they are hidden, and I can't use the 5 individual images visible because they don't quite match together with CSS.

How can I make ng-click to work while the object it is attached to is hidden?