Get the current YouTube video's poster image (highest resolution available) with this simple Bookmarklet

BookMarklet Get YouTube poster image.html

<a href ="javascript:(function()%7Bfunction%20getParameterByName(name)%20%7Bname%20%3D%20name.replace(%2F%5B%5C%5B%5D%2F%2C%20%22%5C%5C%5B%22).replace(%2F%5B%5C%5D%5D%2F%2C%20%22%5C%5C%5D%22)%3Bvar%20regex%20%3D%20new%20RegExp(%22%5B%5C%5C%3F%26%5D%22%20%2B%20name%20%2B%20%22%3D(%5B%5E%26%23%5D*)%22)%2Cresults%20%3D%20regex.exec(location.search)%3Breturn%20results%20%3D%3D%20null%20%3F%20%22%22%20%3A%20decodeURIComponent(results%5B1%5D.replace(%2F%5C%2B%2Fg%2C%20%22%20%22))%3B%7Dvar%20id%20%3D%20getParameterByName%20(%22v%22)%3Bif%20(typeof%20id%20!%3D%3D%20null%20%26%26%20id%20!%3D%3D%22%22)%20%7Bvar%20url%20%3D%20%22http%3A%2F%2Fimg.youtube.com%2Fvi%2F%22%20%2B%20id%20%2B%20%22%2Fmaxresdefault.jpg%22%3Bwindow.open(url%2C'_blank')%3B%7D%20else%20%7Balert%20(%22Activate%20the%20tab%20in%20your%20browser%20where%20the%20YouTube%20video%20is%20loaded%20and%20try%20again!%22)%3B%7D%7D)()">Grab Poster Image</a>

GrabYoutubePosterImageBookMarklet.html

javascript:(function()%7Bfunction%20getParameterByName(name)%20%7Bname%20%3D%20name.replace(%2F%5B%5C%5B%5D%2F%2C%20%22%5C%5C%5B%22).replace(%2F%5B%5C%5D%5D%2F%2C%20%22%5C%5C%5D%22)%3Bvar%20regex%20%3D%20new%20RegExp(%22%5B%5C%5C%3F%26%5D%22%20%2B%20name%20%2B%20%22%3D(%5B%5E%26%23%5D*)%22)%2Cresults%20%3D%20regex.exec(location.search)%3Breturn%20results%20%3D%3D%20null%20%3F%20%22%22%20%3A%20decodeURIComponent(results%5B1%5D.replace(%2F%5C%2B%2Fg%2C%20%22%20%22))%3B%7Dvar%20id%20%3D%20getParameterByName%20(%22v%22)%3Bif%20(typeof%20id%20!%3D%3D%20null%20%26%26%20id%20!%3D%3D%22%22)%20%7Bvar%20url%20%3D%20%22http%3A%2F%2Fimg.youtube.com%2Fvi%2F%22%20%2B%20id%20%2B%20%22%2Fmaxresdefault.jpg%22%3Bwindow.open(url%2C'_blank')%3B%7D%20else%20%7Balert%20(%22Activate%20the%20tab%20in%20your%20browser%20where%20the%20YouTube%20video%20is%20loaded%20and%20try%20again!%22)%3B%7D%7D)()

RawJavascript.js

function getParameterByName(name) {
    name = name.replace(/[\[]/, "\\[").replace(/[\]]/, "\\]");
    var regex = new RegExp("[\\?&]" + name + "=([^&#]*)"),
        results = regex.exec(location.search);
    return results == null ? "" : decodeURIComponent(results[1].replace(/\+/g, " "));
}
var id = getParameterByName ("v");
if (typeof id !== null && id !=="") {
var url = "http://img.youtube.com/vi/" + id + "/maxresdefault.jpg";
window.open(url,'_blank');
} else {
alert ("Activate the tab in your browser where the YouTube video is loaded and try again!");
}