Add a class to 'a' tag
<table><thead><th class="reportgridheader">
<a href="#" class="category">Category</a>
</th></thead></table>
Add JQuery code
$(document).ready(function () {
$('.category').click(function() {
$(this).parent().append( "<img src='' />" );
});
});
If you are looking for background image of parent element, use this code
$(document).ready(function () {
$('.category').click(function() {
$(this).parent().css("background-image", "pathOfTheImage");
});
});