You can use .attr() to get the src
of your image then .append() to append newly created image with retrieved src
to the div with id show-image
:
var src = $('.post-img').attr('src');
$('#show-image').append('<img src="' + src + '" />');
or you can use .appendTo():
var url=$('.post-img').attr("src");
$('<img src="'+url+'" />').appendTo('#show-image');