diff --git a/admin/rt-retranscode-admin.php b/admin/rt-retranscode-admin.php
index 2183874..f7dea3b 100644
--- a/admin/rt-retranscode-admin.php
+++ b/admin/rt-retranscode-admin.php
@@ -78,6 +78,8 @@ public function __construct() {
 		add_filter( 'amp_story_allowed_video_types', array( $this, 'add_amp_video_extensions' ) ); // Extend allowed video mime type extensions for AMP Story Background.
 		add_filter( 'render_block', array( $this, 'update_amp_story_video_url' ), 10, 2 ); // Filter block content and replace video URLs.
 
+		add_filter( 'get_post_metadata', [ $this, 'get_post_thumbnail_metadata' ], 10, 4 );
+
 		// Allow people to change what capability is required to use this feature.
 		$this->capability = apply_filters( 'retranscode_media_cap', 'manage_options' );
 
@@ -806,6 +808,17 @@ public function transcoded_thumbnails_added( $media_id = '' ) {
 			return;
 		}
 
+		// Meta key for meta data, Which store the last generated thumbnail (by transcoder).
+		$last_generated_thumbnail_id_key = 'transcoder_generated_thumbnail_id';
+
+		$last_generated_thumbnail_id = get_post_meta( $media_id, $last_generated_thumbnail_id_key, true );
+		$last_generated_thumbnail_id = ( ! empty( $last_generated_thumbnail_id ) && 0 < intval( $last_generated_thumbnail_id ) ) ? intval( $last_generated_thumbnail_id ) : 0;
+
+		$post_thumbnail_id = get_post_thumbnail_id( $media_id );
+		$post_thumbnail_id = ( ! empty( $post_thumbnail_id ) && 0 < intval( $post_thumbnail_id ) ) ? intval( $post_thumbnail_id ) : 0;
+
+		$has_custom_thumbnail = ( ! empty( $last_generated_thumbnail_id ) && $post_thumbnail_id !== $last_generated_thumbnail_id );
+
 		$is_retranscoding_job = get_post_meta( $media_id, '_rt_retranscoding_sent', true );
 
 		if ( $is_retranscoding_job && ! rtt_is_override_thumbnail() ) {
@@ -858,10 +871,31 @@ public function transcoded_thumbnails_added( $media_id = '' ) {
 
 			// Generate attachment metadata for thumbnail and set post thumbnail for video/audio files.
 			if ( ! is_wp_error( $attachment_id ) && 0 !== $attachment_id ) {
+
+				/**
+				 * Save generated thumbnail ID.
+				 * In additional meta data. so we can identify which if current one is auto generated or custom.
+				 */
+				update_post_meta( $media_id, $last_generated_thumbnail_id_key, $attachment_id );
+
+				/**
+				 * Delete previously generated attachment.
+				 */
+				if ( ! empty( $last_generated_thumbnail_id ) ) {
+					wp_delete_attachment( $last_generated_thumbnail_id );
+				}
+
 				$attach_data = wp_generate_attachment_metadata( $attachment_id, $thumbnail_src );
 				wp_update_attachment_metadata( $attachment_id, $attach_data );
-				set_post_thumbnail( $media_id, $attachment_id );
 				update_post_meta( $attachment_id, 'amp_is_poster', true );
+
+				/**
+				 * Set newly generate thumbnail to attachment only if is was set automatically.
+				 */
+				if ( ! $has_custom_thumbnail ) {
+					set_post_thumbnail( $media_id, $attachment_id );
+				}
+
 			}
 		}
 	}
@@ -1017,6 +1051,42 @@ public function add_search_mime_types( $where ) {
 		return $where;
 	}
 
+	/**
+	 * Set default preview of image attachment is image it self.
+	 *
+	 * @param string|int|array $value    Meta value.
+	 * @param int              $post_id  Post ID.
+	 * @param string           $meta_key Meta key.
+	 * @param bool             $single   If request single value or all the value.
+	 *
+	 * @return string|int|array Meta value.
+	 */
+	public function get_post_thumbnail_metadata( $value, $post_id, $meta_key, $single ) {
+
+		if ( empty( $post_id ) || 0 >= intval( $post_id ) || '_thumbnail_id' !== $meta_key ) {
+			return $value;
+		}
+
+		$post = get_post( $post_id );
+
+		// Only for attachment and if it. We don't want to touch any other post types.
+		if ( empty( $post ) || ! is_a( $post, 'WP_Post' ) || 'attachment' !== $post->post_type || false === strpos( $post->post_mime_type, 'video/' ) ) {
+			return $value;
+		}
+
+		remove_filter( 'get_post_metadata', [ $this, 'get_post_thumbnail_metadata' ], 10 );
+
+		$thumbnail_id = get_post_thumbnail_id( $post_id );
+
+		add_filter( 'get_post_metadata', [ $this, 'get_post_thumbnail_metadata' ], 10, 4 );
+
+		if ( empty( $thumbnail_id ) || 0 >= intval( $thumbnail_id ) ) {
+			$value = get_post_meta( $post_id, 'transcoder_generated_thumbnail_id', $single );
+		}
+
+		return $value;
+	}
+
 }
 
 // Start up this plugin.