$('element_to_add',this).val();

$(this).find("img"); // any img tag child or grandchild etc...
$(this).children("img"); //any img tag child that is direct descendant
$(this).find("img:first") //any img tag first child or first grandchild etc...
$(this).children("img:first") //the first img tag  child that is direct descendant
$(this).children("img:nth-child(1)") //the img is first direct descendant child
$(this).next(); //the img is first direct descendant child

$("#"+$(this).attr("id")+" img:first")