Featured Image, and Image in post

on the template of the page that you are trying to pull the first image on,(if its the post itself, then single.php) you could use the following code instead of the_post_thumbnail

function echo_first_image( $postID ) {
$args = array(
    'numberposts' => 1,
    'order' => 'ASC',
    'post_mime_type' => 'image',
    'post_parent' => $postID,
    'post_status' => null,
    'post_type' => 'attachment',
);

$attachments = get_children( $args );

if ( $attachments ) {
    foreach ( $attachments as $attachment ) {
        $image_attributes = wp_get_attachment_image_src( $attachment->ID, 'thumbnail' )  ? wp_get_attachment_image_src( $attachment->ID, 'thumbnail' ) : wp_get_attachment_image_src( $attachment->ID, 'full' );

        echo '<img src="' . wp_get_attachment_thumb_url( $attachment->ID ) . '" class="current">';
    }
}
}