Untitled

$("#see_comments").click(function() {
    $.post(
        "comments.php",
        {aid: imgnum},
        function (data) {

        }
    );
});

$("#see_comments").click(function() {
  $('<form action="comments.php" method="POST">' +
    '<input type="hidden" name="aid" value="' + imgnum + '">' +
    '</form>').submit();
});

$("#see_comments").click(function () {
    $('<form action="comments.php" method="POST"/>')
        .append($('<input type="hidden" name="aid" value="' + imgnum + '">'))
        .appendTo($(document.body)) //it has to be added somewhere into the <body>
        .submit();
});

<form id='see_comments_form' action='comments.php' action='POST'>
    <input id='see_comments_aid' type='hidden' name='aid' value=''>
</form>

$("#see_comments").click(function(){
    $('#see_comments_aid').val(imgnum);
    $('#see_comments_form').submit();
);

$("#see_comments").attr({href: "comments.php?aid='"+imgnum+"'"});