Kiten,
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<link rel="stylesheet" type="text/css" href="css/normalize.css">
<link rel="stylesheet" type="text/css" href="css/skeleton.css">
<link rel="stylesheet" type="text/css" href="css/main.css">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
<script src="https://code.jquery.com/jquery-2.2.0.min.js" type="text/javascript"></script>
</head>
<body>
<div class="container">
<div class="gallery">
<img src="img/1.jpg" alt="">
<img src="img/2.jpg" alt="">
<img src="img/3.jpg" alt="">
</div>
<button onclick="dp()">BUTTON</button>
</div>
<script>
function dp() {
var x = document.getElementsByTagName("IMG");
var i;
for (i = 0; i < x.length; i++) {
x[i].addEventListener("click", qwerty(i));
}
}
function qwerty(i) {
return function() {
alert(i);
}
}
</script>
</body>
</html>