the_post_thumbnail() echoes the full image tag including src, you’re using it within your own image tag. If you want just the thumbnail src to use within your own tag, use wp_get_attachment_image_src instead.
also- unrelated, use the_title_attribute for alt and title attributes within tags instead of the_title.
EDIT- using wp_get_attachment_image_src:
<?php
$image_attributes = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'full' );
?>
<img src="https://wordpress.stackexchange.com/questions/65447/<?php echo $image_attributes[0] ?>" width="<?php echo $image_attributes[1]; ?>" height="<?php echo $image_attributes[2]; ?>" />