Toggling/Switching Between Multiple Images With OnClick

I have created a long list of items. For each item, there is 1 image. In my case, I use the same image each time.

I would like to use JS to allow users to check an item by clicking on it. Please note, I am not using radio buttons or any other forms.

This is my JS function:

It is triggered using this:

It works for each image. It switches to 2.png when a user clicks on each instance of that image. But how do you make sure it switches back to 1.png on the next click, and so on, effectively creating a switch for multiple instances of the same image?