CSS3 transition on click using pure CSS

Method #1: CSS :focus pseudo-class

As pure CSS solution, you could achieve sort of the effect by using a tabindex attribute for the image, and :focus pseudo-class as follows:

<img class="crossRotate" src="http://placehold.it/100" tabindex="1" />

.crossRotate {
    outline: 0;
    /* other styles... */
}

.crossRotate:focus {
  -webkit-transform: rotate(45deg);
  -ms-transform: rotate(45deg);
  transform: rotate(45deg);
}

WORKING DEMO.

Note: Using this approach, the image gets rotated onclick (focused), to negate the rotation, you'll need to click somewhere out of the image (blured).

Method #2: Hidden input & :checked pseudo-class

This is one of my favorite methods. In this approach, there's a hidden checkbox input and a <label> element which wraps the image.

Once you click on the image, the hidden input is checked because of using for attribute for the label.

Hence by using the :checked pseudo-class and adjacent sibling selector +, we could get the image to be rotated:

<input type="checkbox" id="hacky-input">

<label for="hacky-input">
  <img class="crossRotate" src="http://placehold.it/100">
</label>

#hacky-input {
  display: none; /* Hide the input */
}

#hacky-input:checked + label img.crossRotate {
  -webkit-transform: rotate(45deg);
  -ms-transform: rotate(45deg);
  transform: rotate(45deg);
}

WORKING DEMO #1.

WORKING DEMO #2 (Applying the rotate to the label gives a better experience).

Method #3: Toggling a class via JavaScript

If using JavaScript/jQuery is an option, you could toggle a .active class by .toggleClass() to trigger the rotation effect, as follows:

$('.crossRotate').on('click', function(){
    $(this).toggleClass('active');
});

.crossRotate.active {
    /* vendor-prefixes here... */
    transform: rotate(45deg);
}

WORKING DEMO.

If you want a css only solution you can use active

.crossRotate:active {
   transform: rotate(45deg);
   -webkit-transform: rotate(45deg);
   -ms-transform: rotate(45deg);
}

But the transformation will not persist when the activity moves. For that you need javascript (jquery click and css is the cleanest IMO).

$( ".crossRotate" ).click(function() {
    if (  $( this ).css( "transform" ) == 'none' ){
        $(this).css("transform","rotate(45deg)");
    } else {
        $(this).css("transform","" );
    }
});

Fiddle