diff --git a/core/core.services.yml b/core/core.services.yml
index f5ed5db..ef31454 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -1039,9 +1039,23 @@ services:
   file.mime_type.guesser:
     class: Drupal\Core\File\MimeType\MimeTypeGuesser
     tags:
-      - { name: service_collector, tag: mime_type_guesser, call: addGuesser }
+      - { name: service_collector, tag: mime_type_guesser_extension, call: addGuesser }
+  file.mime_type.guesser.content_based:
+    class: Drupal\Core\File\MimeType\MimeTypeGuesser
+    tags:
+      - { name: service_collector, tag: mime_type_guesser_content_based, call: addGuesser }
   file.mime_type.guesser.extension:
     class: Drupal\Core\File\MimeType\ExtensionMimeTypeGuesser
     arguments: ['@module_handler']
     tags:
-      - { name: mime_type_guesser }
+      - { name: mime_type_guesser_extension }
+      - { name: mime_type_guesser_content_based, priority: 10 }
+  mime_type.guesser.finfo:
+    class: Symfony\Component\HttpFoundation\File\MimeType\FileinfoMimeTypeGuesser
+    tags:
+      - { name: mime_type_guesser_content_based, priority: 30 }
+  mime_type.guesser.binary:
+    class: Symfony\Component\HttpFoundation\File\MimeType\FileBinaryMimeTypeGuesser
+    arguments: ['@module_handler']
+    tags:
+      - { name: mime_type_guesser_content_based, priority: 20 }
diff --git a/core/lib/Drupal/Core/Image/Image.php b/core/lib/Drupal/Core/Image/Image.php
index e170991..727df9d 100644
--- a/core/lib/Drupal/Core/Image/Image.php
+++ b/core/lib/Drupal/Core/Image/Image.php
@@ -34,13 +34,6 @@ class Image implements ImageInterface {
   protected $toolkit;
 
   /**
-   * File size in bytes.
-   *
-   * @var int
-   */
-  protected $fileSize;
-
-  /**
    * Constructs a new Image object.
    *
    * @param \Drupal\Core\ImageToolkit\ImageToolkitInterface $toolkit
@@ -55,9 +48,7 @@ public function __construct(ImageToolkitInterface $toolkit, $source = NULL) {
     if ($source) {
       $this->source = $source;
       // Defer image file validity check to the toolkit.
-      if ($this->getToolkit()->parseFile()) {
-        $this->fileSize = filesize($this->source);
-      }
+      $this->getToolkit()->parseFile();
     }
   }
 
@@ -85,13 +76,6 @@ public function getWidth() {
   /**
    * {@inheritdoc}
    */
-  public function getFileSize() {
-    return $this->fileSize;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
   public function getMimeType() {
     return $this->getToolkit()->getMimeType();
   }
@@ -130,7 +114,6 @@ public function save($destination = NULL) {
     if ($return = $this->getToolkit()->save($destination)) {
       // Clear the cached file size and refresh the image information.
       clearstatcache(TRUE, $destination);
-      $this->fileSize = filesize($destination);
       $this->source = $destination;
 
       // @todo Use File utility when https://drupal.org/node/2050759 is in.
diff --git a/core/lib/Drupal/Core/Image/ImageInterface.php b/core/lib/Drupal/Core/Image/ImageInterface.php
index 02db478..525b931 100644
--- a/core/lib/Drupal/Core/Image/ImageInterface.php
+++ b/core/lib/Drupal/Core/Image/ImageInterface.php
@@ -37,14 +37,6 @@ public function getHeight();
   public function getWidth();
 
   /**
-   * Returns the size of the image file.
-   *
-   * @return int|null
-   *   The size of the file in bytes, or NULL if the image is invalid.
-   */
-  public function getFileSize();
-
-  /**
    * Returns the MIME type of the image file.
    *
    * @return string
diff --git a/core/modules/file/file.module b/core/modules/file/file.module
index a516836..62e924e 100644
--- a/core/modules/file/file.module
+++ b/core/modules/file/file.module
@@ -462,7 +462,7 @@ function file_validate_image_resolution(FileInterface $file, $maximum_dimensions
         // Try to resize the image to fit the dimensions.
         if ($image->scale($width, $height)) {
           $image->save();
-          $file->filesize = $image->getFileSize();
+          $file->setSize(filesize($file->getFileUri()));
           drupal_set_message(t('The image was resized to fit within the maximum allowed dimensions of %dimensions pixels.', array('%dimensions' => $maximum_dimensions)));
         }
         else {
diff --git a/core/modules/image/image.module b/core/modules/image/image.module
index 913fb7f..df0b675 100644
--- a/core/modules/image/image.module
+++ b/core/modules/image/image.module
@@ -156,6 +156,13 @@ function image_theme() {
  * Implements hook_file_download().
  *
  * Control the access to files underneath the styles directory.
+ *
+ * The ImageStyleDownloadController does not call this hook when it is about to
+ * create a derivative. Thus for files under the styles directory, this hook is
+ * only called when the derivative already exists.
+ *
+ * This hook allows access if the user has access to the original and denies
+ * access when the user has not access to the original.
  */
 function image_file_download($uri) {
   $path = file_uri_target($uri);
@@ -170,25 +177,23 @@ function image_file_download($uri) {
     // Then the remaining parts are the path to the image.
     $original_uri = file_uri_scheme($uri) . '://' . implode('/', $args);
 
-    // Check that the file exists and is an image.
-    $image = \Drupal::service('image.factory')->get($uri);
-    if ($image->isValid()) {
-      // Check the permissions of the original to grant access to this image.
-      $headers = \Drupal::moduleHandler()->invokeAll('file_download', array($original_uri));
-      // Confirm there's at least one module granting access and none denying access.
-      if (!empty($headers) && !in_array(-1, $headers)) {
-        return array(
-          // Send headers describing the image's size, and MIME-type...
-          'Content-Type' => $image->getMimeType(),
-          'Content-Length' => $image->getFileSize(),
-          // By not explicitly setting them here, this uses normal Drupal
-          // Expires, Cache-Control and ETag headers to prevent proxy or
-          // browser caching of private images.
-        );
-      }
+    // Check the permissions of the original to grant access to this image.
+    $headers = \Drupal::moduleHandler()->invokeAll('file_download', array($original_uri));
+    // Confirm there's at least one module granting access and none denying access.
+    if (!empty($headers) && !in_array(-1, $headers)) {
+      return array(
+        // Send headers describing the image's size and MIME type.
+        'Content-Type' => \Drupal::service('file.mime_type.guesser.content_based')->guess($uri),
+        'Content-Length' => filesize($uri),
+        // By not explicitly setting cache related headers here, this uses
+        // normal Drupal Expires, Cache-Control and ETag headers to prevent
+        // proxy or browser caching of private images.
+      );
     }
     return -1;
   }
+  // We don't want a say over files outside the styles directory.
+  return NULL;
 }
 
 /**
diff --git a/core/modules/image/src/Controller/ImageStyleDownloadController.php b/core/modules/image/src/Controller/ImageStyleDownloadController.php
index a18c677..6b5ef30 100644
--- a/core/modules/image/src/Controller/ImageStyleDownloadController.php
+++ b/core/modules/image/src/Controller/ImageStyleDownloadController.php
@@ -8,13 +8,13 @@
 namespace Drupal\image\Controller;
 
 use Drupal\Component\Utility\Crypt;
-use Drupal\Core\Image\ImageFactory;
 use Drupal\Core\Lock\LockBackendInterface;
 use Drupal\image\ImageStyleInterface;
 use Drupal\system\FileDownloadController;
 use Psr\Log\LoggerInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\HttpFoundation\BinaryFileResponse;
+use Symfony\Component\HttpFoundation\File\MimeType\MimeTypeGuesserInterface;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException;
@@ -33,11 +33,11 @@ class ImageStyleDownloadController extends FileDownloadController {
   protected $lock;
 
   /**
-   * The image factory.
+   * The MIME type guesser.
    *
-   * @var \Drupal\Core\Image\ImageFactory
+   * @var \Symfony\Component\HttpFoundation\File\MimeType\MimeTypeGuesserInterface
    */
-  protected $imageFactory;
+  protected $mimeTypeGuesser;
 
   /**
    * A logger instance.
@@ -51,14 +51,14 @@ class ImageStyleDownloadController extends FileDownloadController {
    *
    * @param \Drupal\Core\Lock\LockBackendInterface $lock
    *   The lock backend.
-   * @param \Drupal\Core\Image\ImageFactory $image_factory
-   *   The image factory.
+   * @param \Symfony\Component\HttpFoundation\File\MimeType\MimeTypeGuesserInterface $mimeTypeGuesser
+   *   The MIME type guesser.
    * @param \Psr\Log\LoggerInterface $logger
    *   A logger instance.
    */
-  public function __construct(LockBackendInterface $lock, ImageFactory $image_factory, LoggerInterface $logger) {
+  public function __construct(LockBackendInterface $lock, MimeTypeGuesserInterface $mimeTypeGuesser, LoggerInterface $logger) {
     $this->lock = $lock;
-    $this->imageFactory = $image_factory;
+    $this->mimeTypeGuesser = $mimeTypeGuesser;
     $this->logger = $logger;
   }
 
@@ -68,7 +68,7 @@ public function __construct(LockBackendInterface $lock, ImageFactory $image_fact
   public static function create(ContainerInterface $container) {
     return new static(
       $container->get('lock'),
-      $container->get('image.factory'),
+      $container->get('file.mime_type.guesser.content_based'),
       $container->get('logger.factory')->get('image')
     );
   }
@@ -155,13 +155,11 @@ public function deliver(Request $request, $scheme, ImageStyleInterface $image_st
     }
 
     if ($success) {
-      $image = $this->imageFactory->get($derivative_uri);
-      $uri = $image->getSource();
       $headers += array(
-        'Content-Type' => $image->getMimeType(),
-        'Content-Length' => $image->getFileSize(),
+        'Content-Type' => $this->mimeTypeGuesser->guess($derivative_uri),
+        'Content-Length' => filesize($derivative_uri),
       );
-      return new BinaryFileResponse($uri, 200, $headers);
+      return new BinaryFileResponse($derivative_uri, 200, $headers);
     }
     else {
       $this->logger->notice('Unable to generate the derived image located at %path.', array('%path' => $derivative_uri));
diff --git a/core/modules/image/src/Entity/ImageStyle.php b/core/modules/image/src/Entity/ImageStyle.php
index 0579dbc..8d77622 100644
--- a/core/modules/image/src/Entity/ImageStyle.php
+++ b/core/modules/image/src/Entity/ImageStyle.php
@@ -196,7 +196,7 @@ public function buildUrl($path, $clean_urls = NULL) {
     // 'image.settings:suppress_itok_output' configuration to TRUE to achieve
     // that (if both are set, the security token will neither be emitted in the
     // image derivative URL nor checked for in
-    // \Drupal\image\ImageStyleInterface::deliver()).
+    // \Drupal\image\Controller\ImageStyleDownloadController::deliver()).
     $token_query = array();
     if (!\Drupal::config('image.settings')->get('suppress_itok_output')) {
       // The passed $path variable can be either a relative path or a full URI.
diff --git a/core/modules/image/src/Tests/ImageStylesPathAndUrlTest.php b/core/modules/image/src/Tests/ImageStylesPathAndUrlTest.php
index b57ce9f..0f04199 100644
--- a/core/modules/image/src/Tests/ImageStylesPathAndUrlTest.php
+++ b/core/modules/image/src/Tests/ImageStylesPathAndUrlTest.php
@@ -173,9 +173,8 @@ function doImageStyleUrlAndPathTests($scheme, $clean_url = TRUE, $extra_slash =
     $this->assertResponse(200, 'Image was generated at the URL.');
     $this->assertTrue(file_exists($generated_uri), 'Generated file does exist after we accessed it.');
     $this->assertRaw(file_get_contents($generated_uri), 'URL returns expected file.');
-    $image = $this->container->get('image.factory')->get($generated_uri);
-    $this->assertEqual($this->drupalGetHeader('Content-Type'), $image->getMimeType(), 'Expected Content-Type was reported.');
-    $this->assertEqual($this->drupalGetHeader('Content-Length'), $image->getFileSize(), 'Expected Content-Length was reported.');
+    $this->assertEqual($this->drupalGetHeader('Content-Type'), $this->container->get('file.mime_type.guesser.content_based')->guess($generated_uri), 'Expected Content-Type was reported.');
+    $this->assertEqual($this->drupalGetHeader('Content-Length'), filesize($generated_uri), 'Expected Content-Length was reported.');
     if ($scheme == 'private') {
       $this->assertEqual($this->drupalGetHeader('Expires'), 'Sun, 19 Nov 1978 05:00:00 GMT', 'Expires header was sent.');
       $this->assertNotEqual(strpos($this->drupalGetHeader('Cache-Control'), 'no-cache'), FALSE, 'Cache-Control header contains \'no-cache\' to prevent caching.');
diff --git a/core/tests/Drupal/Tests/Core/Image/ImageTest.php b/core/tests/Drupal/Tests/Core/Image/ImageTest.php
index fa91f28..4ecaad2 100644
--- a/core/tests/Drupal/Tests/Core/Image/ImageTest.php
+++ b/core/tests/Drupal/Tests/Core/Image/ImageTest.php
@@ -162,14 +162,6 @@ public function testGetWidth() {
   }
 
   /**
-   * Tests \Drupal\Core\Image\Image::getFileSize
-   */
-  public function testGetFileSize() {
-    $this->getTestImage(FALSE);
-    $this->assertEquals(3905, $this->image->getFileSize());
-  }
-
-  /**
    * Tests \Drupal\Core\Image\Image::getToolkit()->getType().
    */
   public function testGetType() {