New Trait for decoding attribute in images

system/blueprints/config/system.yaml

@@ -1300,6 +1300,17 @@ form:
                 auto: Auto
                 lazy: Lazy
                 eager: Eager
+
+            images.defaults.decoding:
+              type: select
+              size: small
+              label: PLUGIN_ADMIN.IMAGES_DECODING
+              help: PLUGIN_ADMIN.IMAGES_DECODING_HELP
+              highlight: auto
+              options:
+                auto: Auto
+                sync: Sync
+                async: Async
 
             images.seofriendly:
               type: toggle

system/config/system.yaml

@@ -168,6 +168,7 @@ images:
     retina_scale: 1                              # scale to adjust auto-sizes for better handling of HiDPI resolutions
   defaults:
     loading: auto                                # Let browser pick [auto|lazy|eager]
+    decoding: auto                               # Let browser pick [auto|sync|async]
   watermark:
     image: 'system://images/watermark.png'       # Path to a watermark image
     position_y: 'center'                         # top|center|bottom

system/src/Grav/Common/Media/Traits/ImageDecodingTrait.php

@@ -0,0 +1,40 @@
+<?php
+
+/**
+ * @package    Grav\Common\Media
+ * @author     Pedro Moreno https://github.com/pmoreno-rodriguez
+ * @license    MIT License; see LICENSE file for details.
+ */
+
+namespace Grav\Common\Media\Traits;
+
+use Grav\Common\Grav;
+
+/**
+ * Trait ImageDecodingTrait
+ * @package Grav\Common\Media\Traits
+ */
+
+trait ImageDecodingTrait
+{
+    /**
+     * Allows to set the decoding attribute from Markdown or Twig
+     *
+     * @param string|null $value
+     * @return $this
+     */
+    public function decoding($value = null)
+    {
+        if (null === $value) {
+            $value = Grav::instance()['config']->get('system.images.defaults.decoding', 'auto');
+        }
+
+        // Validate the provided value (similar to loading)
+        if ($value !== null && $value !== 'auto') {
+            $this->attributes['decoding'] = $value;
+        }
+
+        return $this;
+    }
+
+}

system/src/Grav/Common/Page/Medium/ImageMedium.php

@@ -15,6 +15,7 @@
 use Grav\Common\Media\Interfaces\ImageMediaInterface;
 use Grav\Common\Media\Interfaces\MediaLinkInterface;
 use Grav\Common\Media\Traits\ImageLoadingTrait;
+use Grav\Common\Media\Traits\ImageDecodingTrait;
 use Grav\Common\Media\Traits\ImageMediaTrait;
 use Grav\Common\Utils;
 use Gregwar\Image\Image;
@@ -30,6 +31,7 @@ class ImageMedium extends Medium implements ImageMediaInterface, ImageManipulate
 {
     use ImageMediaTrait;
     use ImageLoadingTrait;
+    use ImageDecodingTrait;
 
     /**
      * @var mixed|string