Hi Alessia,
mhm. Not really. You cannot work with pure CSS.
jQuery is actually made for exactly those interactions.
Ok, I solved it for you in a way.
If you want to get more specific or into detail you should make a jQuery course at Codeacademy. Very useful in general.
Here we go:
The Button Text will be the button. The image is hidden and will be visible on click.

You give the button the class .button
and the image the class .hide
.


Then in the custom HTML section you will add the following in the CSS box:
.hide {
display: none;
}
.show {
display: block !important;
}
And this in the Custom Head Content box:
<script>
jQuery(document).on("click", ".button", function(event) {
jQuery(".hide").toggleClass("show");
});
</script>
That should work. it is the basic. From there on you can built it up yourself.
All the best!
Marius