JSFiddle - React, Tailwind, and code Playground

HTML

<div class="img_container">
    <img src="http://ynternet.sk/test/bg_1.png" class='img_keep' />
    <br />
    <input type="checkbox" name="bg_1.jpg" id="bg_1.jpg"  />
</div>
<div class="img_container">
    <img src="http://ynternet.sk/test/bg_2.png" class='img_keep' />
    <br />
    <input type="checkbox" name="bg_2.jpg" id="bg_2.jpg" />
</div>
<div class="img_container">
    <img src="http://ynternet.sk/test/bg_3.png" class='img_keep' />
    <br />
    <input type="checkbox" name="bg_3.jpg" id="bg_3.jpg" />
</div>
<hr />
<input type="text" value="" name="delete_these" id="delete_these" style='width: 300px;' />

CSS

.img_container {
    padding:5px;
    display:inline-block;
}
.img_keep {
  border: 2px solid gray;
}
.img_del {
  border: 2px solid red;
}

JavaScript

window.addEvent('domready', function() {
    var checks, del, delete_these;
    checks = $$('input[type="checkbox"]');
    delete_these = $('delete_these');
    del = [];
    checks.each(function (item) {
        item.addEvent('change', function(event) {
            markHidden(event.target);
        });
        markHidden(item);
    });

    function markHidden(el) {
        var id, del_string, img;
        id = el.getProperty('id');
        img = el.getParent().getFirst('img');
        if (el.checked) {
            del.include(id);
            img.tween('border-color', 'gray', 'red');
        } else {
            del.erase(id);
            img.tween('border-color', 'red', 'gray');
        }
        del_string = JSON.encode(del);
        delete_these.value = JSON.encode(del);
    }
});