Fallback to closest match if size changes.

includes/class-wc-regenerate-images.php

@@ -78,7 +78,17 @@ class WC_Regenerate_Images {
 			return $data;
 		}
 
+		// See if the image size has changed from our settings.
 		if ( ! self::image_size_matches_settings( $data, $size ) ) {
+			// If Photon is running we can just return false and let Jetpack handle regeneration.
+			if ( class_exists( 'Jetpack' ) && Jetpack::is_module_active( 'photon' ) ) {
+				return false;
+			} else {
+				// If we get here, Jetpack is not running and we don't have the correct image sized stored. Try to return closest match.
+				$size_data = wc_get_image_size( $size );
+				return image_get_intermediate_size( $attachment_id, array( absint( $size_data['width'] ), absint( $size_data['height'] ) ) );
+			}
+
 			return false;
 		}