diff --git a/src/wp-includes/block-supports/background.php b/src/wp-includes/block-supports/background.php
index c1b3d4d0940fa..e3873e9783373 100644
--- a/src/wp-includes/block-supports/background.php
+++ b/src/wp-includes/block-supports/background.php
@@ -41,6 +41,8 @@ function wp_register_background_support( $block_type ) {
  *
  * @since 6.4.0
  * @since 6.5.0 Added support for `backgroundPosition` and `backgroundRepeat` output.
+ * @since 6.6.0 Removed requirement for `backgroundImage.source`. A file/url is the default.
+ *
  * @access private
  *
  * @param  string $block_content Rendered block content.
@@ -61,10 +63,10 @@ function wp_render_background_support( $block_content, $block ) {
 	}
 
 	$background_styles                    = array();
-	$background_styles['backgroundSize']  = isset( $block_attributes['style']['background']['backgroundSize'] ) ? $block_attributes['style']['background']['backgroundSize'] : 'cover';
 	$background_styles['backgroundImage'] = isset( $block_attributes['style']['background']['backgroundImage'] ) ? $block_attributes['style']['background']['backgroundImage'] : array();
 
-	if ( isset( $background_styles['backgroundImage']['source'] ) && 'file' === $background_styles['backgroundImage']['source'] && isset( $background_styles['backgroundImage']['url'] ) ) {
+	if ( isset( $background_styles['backgroundImage']['url'] ) ) {
+		$background_styles['backgroundSize']     = isset( $block_attributes['style']['background']['backgroundSize'] ) ? $block_attributes['style']['background']['backgroundSize'] : 'cover';
 		$background_styles['backgroundPosition'] = isset( $block_attributes['style']['background']['backgroundPosition'] ) ? $block_attributes['style']['background']['backgroundPosition'] : null;
 		$background_styles['backgroundRepeat']   = isset( $block_attributes['style']['background']['backgroundRepeat'] ) ? $block_attributes['style']['background']['backgroundRepeat'] : null;
 
diff --git a/src/wp-includes/class-wp-theme-json.php b/src/wp-includes/class-wp-theme-json.php
index 3aeec633da7a0..eca9ff971c5a5 100644
--- a/src/wp-includes/class-wp-theme-json.php
+++ b/src/wp-includes/class-wp-theme-json.php
@@ -303,7 +303,6 @@ class WP_Theme_JSON {
 		),
 		'background-image' => array(
 			array( 'background', 'backgroundImage', 'url' ),
-			array( 'background', 'backgroundImage', 'source' ),
 		),
 	);
 
diff --git a/tests/phpunit/tests/block-supports/wpRenderBackgroundSupport.php b/tests/phpunit/tests/block-supports/wpRenderBackgroundSupport.php
index 83ea7cd47c972..4d2a6cd5b34f8 100644
--- a/tests/phpunit/tests/block-supports/wpRenderBackgroundSupport.php
+++ b/tests/phpunit/tests/block-supports/wpRenderBackgroundSupport.php
@@ -68,6 +68,7 @@ public function filter_set_theme_root() {
 	 *
 	 * @ticket 59357
 	 * @ticket 60175
+	 * @ticket 61123
 	 *
 	 * @covers ::wp_render_background_support
 	 *
@@ -132,8 +133,7 @@ public function data_background_block_support() {
 				),
 				'background_style'    => array(
 					'backgroundImage' => array(
-						'url'    => 'https://example.com/image.jpg',
-						'source' => 'file',
+						'url' => 'https://example.com/image.jpg',
 					),
 				),
 				'expected_wrapper'    => '<div class="has-background" style="background-image:url(&#039;https://example.com/image.jpg&#039;);background-size:cover;">Content</div>',
@@ -147,8 +147,7 @@ public function data_background_block_support() {
 				),
 				'background_style'    => array(
 					'backgroundImage'  => array(
-						'url'    => 'https://example.com/image.jpg',
-						'source' => 'file',
+						'url' => 'https://example.com/image.jpg',
 					),
 					'backgroundRepeat' => 'no-repeat',
 					'backgroundSize'   => 'contain',
@@ -164,8 +163,7 @@ public function data_background_block_support() {
 				),
 				'background_style'    => array(
 					'backgroundImage' => array(
-						'url'    => 'https://example.com/image.jpg',
-						'source' => 'file',
+						'url' => 'https://example.com/image.jpg',
 					),
 				),
 				'expected_wrapper'    => '<div class="wp-block-test has-background" style="color: red;background-image:url(&#039;https://example.com/image.jpg&#039;);background-size:cover;">Content</div>',
@@ -179,8 +177,7 @@ public function data_background_block_support() {
 				),
 				'background_style'    => array(
 					'backgroundImage' => array(
-						'url'    => 'https://example.com/image.jpg',
-						'source' => 'file',
+						'url' => 'https://example.com/image.jpg',
 					),
 				),
 				'expected_wrapper'    => '<div class="wp-block-test has-background" style="color: red;font-size: 15px;background-image:url(&#039;https://example.com/image.jpg&#039;);background-size:cover;">Content</div>',
@@ -194,8 +191,7 @@ public function data_background_block_support() {
 				),
 				'background_style'    => array(
 					'backgroundImage' => array(
-						'url'    => 'https://example.com/image.jpg',
-						'source' => 'file',
+						'url' => 'https://example.com/image.jpg',
 					),
 				),
 				'expected_wrapper'    => '<div>Content</div>',
diff --git a/tests/phpunit/tests/theme/wpThemeJson.php b/tests/phpunit/tests/theme/wpThemeJson.php
index 2eefaf363ba1c..398207f52ad1c 100644
--- a/tests/phpunit/tests/theme/wpThemeJson.php
+++ b/tests/phpunit/tests/theme/wpThemeJson.php
@@ -4921,6 +4921,8 @@ public function test_get_shadow_styles_for_blocks() {
 	}
 
 	/**
+	 * Tests that theme background image styles are correctly generated.
+	 *
 	 * @ticket 61123
 	 */
 	public function test_get_top_level_background_image_styles() {
@@ -4940,8 +4942,7 @@ public function test_get_top_level_background_image_styles() {
 						'core/paragraph' => array(
 							'background' => array(
 								'backgroundImage'    => array(
-									'url'    => 'http://example.org/image.png',
-									'source' => 'file',
+									'url' => 'http://example.org/image.png',
 								),
 								'backgroundSize'     => 'cover',
 								'backgroundRepeat'   => 'no-repeat',