Get a specific tag

I'm trying here to get the previous "img" tag when clicking on the 3rd "i" tag :

<div>
    <img src="img/image1.jpg" alt="image2"/>
    <div id="image_options">
        <i class="material-icons md-36">account_box</i>
        <label>djbaptou</label>
        <div id="left_icons">
            <i class="material-icons md-36 fav">favorite_border</i>
            <i class="material-icons md-36 purple">question_answer</i>
            <i class="material-icons md-36 full_screen">settings_overscan</i>
        </div>
    </div>
</div>

Here is my jQuery code :

$(".full_screen").click(function(){
    var img = $(this).parent().parent().closest("img");
    modal.css("display", "block");
    modalImg.attr("src", img.attr("src"));
});

But when i do a "alert(img);" it says that this is undefined

Any ideas ?