<div  class="bar2 col-md-3">
<input type="hidden" value="<?=$value['id_task'];?>">
<img class="delete_icon" src="/media/img/Delete_icon.png" >
</div>

var elems = document.getElementsByClassName('delete_icon');
        elems.addEventListener('click', function(this){

var input_value = this???
})

<script>
	document.querySelector('.delete_icon').addEventListener('click', function () {
		var val = this.previousElementSibling.value;

		console.log(val);
	}, false);	
</script>