added background_images to configuration

DependencyInjection/Configuration.php

@@ -44,6 +44,7 @@ class Configuration implements ConfigurationInterface
                 ->scalarNode('interpolation')->defaultValue(true)->end()
                 ->arrayNode('text_color')->prototype('scalar')->end()->end()
                 ->arrayNode('background_color')->prototype('scalar')->end()->end()
+                ->arrayNode('background_images')->prototype('scalar')->end()->end()
             ->end()
         ;
 

Generator/CaptchaGenerator.php

@@ -120,6 +120,9 @@ class CaptchaGenerator
 
         $fingerprint = isset($options['fingerprint']) ? $options['fingerprint'] : null;
 
+        // set background images
+        $this->builder->setBackgroundImages($options['background_images']);
+
         $content = $this->builder->build(
             $options['width'],
             $options['height'],