diff --git a/app/code/Magento/Cms/Model/Wysiwyg/Images/Storage.php b/app/code/Magento/Cms/Model/Wysiwyg/Images/Storage.php
index ae88b24bd2682..0cc108e5bed8b 100644
--- a/app/code/Magento/Cms/Model/Wysiwyg/Images/Storage.php
+++ b/app/code/Magento/Cms/Model/Wysiwyg/Images/Storage.php
@@ -22,6 +22,7 @@
  * @SuppressWarnings(PHPMD.TooManyFields)
  * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
  * @SuppressWarnings(PHPMD.CookieAndSessionMisuse)
+ * @SuppressWarnings(PHPMD.ExcessiveClassComplexity)
  *
  * @api
  * @since 100.0.2
@@ -152,6 +153,11 @@ class Storage extends \Magento\Framework\DataObject
      */
     private $ioFile;
 
+    /**
+     * @var \Magento\Framework\File\Mime|null
+     */
+    private $mime;
+
     /**
      * Construct
      *
@@ -174,6 +180,7 @@ class Storage extends \Magento\Framework\DataObject
      * @param \Magento\Framework\Filesystem\DriverInterface $file
      * @param \Magento\Framework\Filesystem\Io\File|null $ioFile
      * @param \Psr\Log\LoggerInterface|null $logger
+     * @param \Magento\Framework\File\Mime $mime
      *
      * @throws \Magento\Framework\Exception\FileSystemException
      * @SuppressWarnings(PHPMD.ExcessiveParameterList)
@@ -197,7 +204,8 @@ public function __construct(
         array $data = [],
         \Magento\Framework\Filesystem\DriverInterface $file = null,
         \Magento\Framework\Filesystem\Io\File $ioFile = null,
-        \Psr\Log\LoggerInterface $logger = null
+        \Psr\Log\LoggerInterface $logger = null,
+        \Magento\Framework\File\Mime $mime = null
     ) {
         $this->_session = $session;
         $this->_backendUrl = $backendUrl;
@@ -217,6 +225,7 @@ public function __construct(
         $this->_dirs = $dirs;
         $this->file = $file ?: ObjectManager::getInstance()->get(\Magento\Framework\Filesystem\Driver\File::class);
         $this->ioFile = $ioFile ?: ObjectManager::getInstance()->get(\Magento\Framework\Filesystem\Io\File::class);
+        $this->mime = $mime ?: ObjectManager::getInstance()->get(\Magento\Framework\File\Mime::class);
         parent::__construct($data);
     }
 
@@ -362,7 +371,7 @@ public function getFilesCollection($path, $type = null)
             $item->setUrl($this->_cmsWysiwygImages->getCurrentUrl() . $item->getBasename());
             $itemStats = $this->file->stat($item->getFilename());
             $item->setSize($itemStats['size']);
-            $item->setMimeType(\mime_content_type($item->getFilename()));
+            $item->setMimeType($this->mime->getMimeType($item->getFilename()));
 
             if ($this->isImage($item->getBasename())) {
                 $thumbUrl = $this->getThumbnailUrl($item->getFilename(), true);
@@ -647,7 +656,7 @@ public function resizeFile($source, $keepRatio = true)
         $image->keepAspectRatio($keepRatio);
 
         list($imageWidth, $imageHeight) = $this->getResizedParams($source);
-        
+
         $image->resize($imageWidth, $imageHeight);
         $dest = $targetDir . '/' . $this->ioFile->getPathInfo($source)['basename'];
         $image->save($dest);
@@ -670,7 +679,7 @@ private function getResizedParams(string $source): array
 
         //phpcs:ignore Generic.PHP.NoSilencedErrors
         list($imageWidth, $imageHeight) = @getimagesize($source);
-     
+
         if ($imageWidth && $imageHeight) {
             $imageWidth = $configWidth > $imageWidth ? $imageWidth : $configWidth;
             $imageHeight = $configHeight > $imageHeight ? $imageHeight : $configHeight;
@@ -679,7 +688,7 @@ private function getResizedParams(string $source): array
         }
         return [$configWidth, $configHeight];
     }
-    
+
     /**
      * Resize images on the fly in controller action
      *
diff --git a/dev/tests/integration/testsuite/Magento/Cms/Model/Wysiwyg/Images/StorageTest.php b/dev/tests/integration/testsuite/Magento/Cms/Model/Wysiwyg/Images/StorageTest.php
index a68a546c20bc6..cb96ca2a14cac 100644
--- a/dev/tests/integration/testsuite/Magento/Cms/Model/Wysiwyg/Images/StorageTest.php
+++ b/dev/tests/integration/testsuite/Magento/Cms/Model/Wysiwyg/Images/StorageTest.php
@@ -6,7 +6,13 @@
  */
 namespace Magento\Cms\Model\Wysiwyg\Images;
 
+use Magento\Cms\Model\Wysiwyg\Images\Storage\Collection;
 use Magento\Framework\App\Filesystem\DirectoryList;
+use Magento\Framework\DataObject;
+use Magento\Framework\Filesystem;
+use Magento\Framework\Filesystem\Driver\File;
+use Magento\Framework\Filesystem\DriverInterface;
+use Magento\TestFramework\Helper\Bootstrap;
 
 /**
  * Test methods of class Storage
@@ -29,22 +35,27 @@ class StorageTest extends \PHPUnit\Framework\TestCase
     private $objectManager;
 
     /**
-     * @var \Magento\Framework\Filesystem
+     * @var Filesystem
      */
     private $filesystem;
 
     /**
-     * @var \Magento\Cms\Model\Wysiwyg\Images\Storage
+     * @var Storage
      */
     private $storage;
 
+    /**
+     * @var DriverInterface
+     */
+    private $driver;
+
     /**
      * @inheritdoc
      */
     // phpcs:disable
     public static function setUpBeforeClass(): void
     {
-        self::$_baseDir = \Magento\TestFramework\Helper\Bootstrap::getObjectManager()->get(
+        self::$_baseDir = Bootstrap::getObjectManager()->get(
             \Magento\Cms\Helper\Wysiwyg\Images::class
         )->getCurrentPath() . 'MagentoCmsModelWysiwygImagesStorageTest';
         if (!file_exists(self::$_baseDir)) {
@@ -60,8 +71,8 @@ public static function setUpBeforeClass(): void
     // phpcs:ignore
     public static function tearDownAfterClass(): void
     {
-        \Magento\TestFramework\Helper\Bootstrap::getObjectManager()->create(
-            \Magento\Framework\Filesystem\Driver\File::class
+        Bootstrap::getObjectManager()->create(
+            File::class
         )->deleteDirectory(
             self::$_baseDir
         );
@@ -72,9 +83,10 @@ public static function tearDownAfterClass(): void
      */
     protected function setUp(): void
     {
-        $this->objectManager = \Magento\TestFramework\Helper\Bootstrap::getObjectManager();
-        $this->filesystem = $this->objectManager->get(\Magento\Framework\Filesystem::class);
-        $this->storage = $this->objectManager->create(\Magento\Cms\Model\Wysiwyg\Images\Storage::class);
+        $this->objectManager = Bootstrap::getObjectManager();
+        $this->filesystem = $this->objectManager->get(Filesystem::class);
+        $this->storage = $this->objectManager->create(Storage::class);
+        $this->driver = Bootstrap::getObjectManager()->get(DriverInterface::class);
     }
 
     /**
@@ -83,16 +95,31 @@ protected function setUp(): void
      */
     public function testGetFilesCollection(): void
     {
-        \Magento\TestFramework\Helper\Bootstrap::getInstance()
+        Bootstrap::getInstance()
             ->loadArea(\Magento\Backend\App\Area\FrontNameResolver::AREA_CODE);
-        $collection = $this->storage->getFilesCollection(self::$_baseDir, 'media');
-        $this->assertInstanceOf(\Magento\Cms\Model\Wysiwyg\Images\Storage\Collection::class, $collection);
+        $fileName = 'magento_image.jpg';
+        $imagePath = realpath(__DIR__ . '/../../../../Catalog/_files/' . $fileName);
+        $mediaDirectory = $this->filesystem->getDirectoryWrite(DirectoryList::MEDIA);
+        $modifiableFilePath = $mediaDirectory->getAbsolutePath('MagentoCmsModelWysiwygImagesStorageTest/' . $fileName);
+        $this->driver->copy(
+            $imagePath,
+            $modifiableFilePath
+        );
+        $this->storage->resizeFile($modifiableFilePath);
+        $collection = $this->storage->getFilesCollection(self::$_baseDir, 'image');
+        $this->assertInstanceOf(Collection::class, $collection);
         foreach ($collection as $item) {
-            $this->assertInstanceOf(\Magento\Framework\DataObject::class, $item);
-            $this->assertStringEndsWith('/1.swf', $item->getUrl());
-            $this->assertStringMatchesFormat(
-                'http://%s/static/%s/adminhtml/%s/%s/Magento_Cms/images/placeholder_thumbnail.jpg',
-                $item->getThumbUrl()
+            $this->assertInstanceOf(DataObject::class, $item);
+            $this->assertStringEndsWith('/' . $fileName, $item->getUrl());
+            $this->assertEquals(
+                '/pub/media/.thumbsMagentoCmsModelWysiwygImagesStorageTest/magento_image.jpg',
+                parse_url($item->getThumbUrl(), PHP_URL_PATH),
+                "Check if Thumbnail URL is equal to the generated URL"
+            );
+            $this->assertEquals(
+                'image/jpeg',
+                $item->getMimeType(),
+                "Check if Mime Type is equal to the image in the file system"
             );
             return;
         }
@@ -121,7 +148,7 @@ public function testDeleteDirectory(): void
         $this->storage->createDirectory($dir, $path);
         $this->assertFileExists($fullPath);
         $this->storage->deleteDirectory($fullPath);
-        $this->assertFileNotExists($fullPath);
+        $this->assertFileDoesNotExist($fullPath);
     }
 
     /**
@@ -142,7 +169,7 @@ public function testDeleteDirectoryWithExcludedDirPath(): void
     public function testUploadFile(): void
     {
         $fileName = 'magento_small_image.jpg';
-        $tmpDirectory = $this->filesystem->getDirectoryWrite(\Magento\Framework\App\Filesystem\DirectoryList::SYS_TMP);
+        $tmpDirectory = $this->filesystem->getDirectoryWrite(DirectoryList::SYS_TMP);
         $filePath = $tmpDirectory->getAbsolutePath($fileName);
         // phpcs:disable
         $fixtureDir = realpath(__DIR__ . '/../../../../Catalog/_files');
@@ -172,7 +199,7 @@ public function testUploadFileWithExcludedDirPath(): void
         );
 
         $fileName = 'magento_small_image.jpg';
-        $tmpDirectory = $this->filesystem->getDirectoryWrite(\Magento\Framework\App\Filesystem\DirectoryList::SYS_TMP);
+        $tmpDirectory = $this->filesystem->getDirectoryWrite(DirectoryList::SYS_TMP);
         $filePath = $tmpDirectory->getAbsolutePath($fileName);
         // phpcs:disable
         $fixtureDir = realpath(__DIR__ . '/../../../../Catalog/_files');
@@ -204,7 +231,7 @@ public function testUploadFileWithWrongExtension(string $fileName, string $fileT
         $this->expectException(\Magento\Framework\Exception\LocalizedException::class);
         $this->expectExceptionMessage('File validation failed.');
 
-        $tmpDirectory = $this->filesystem->getDirectoryWrite(\Magento\Framework\App\Filesystem\DirectoryList::SYS_TMP);
+        $tmpDirectory = $this->filesystem->getDirectoryWrite(DirectoryList::SYS_TMP);
         $filePath = $tmpDirectory->getAbsolutePath($fileName);
         // phpcs:disable
         $fixtureDir = realpath(__DIR__ . '/../../../_files');
@@ -251,7 +278,7 @@ public function testUploadFileWithWrongFile(): void
         $this->expectExceptionMessage('File validation failed.');
 
         $fileName = 'file.gif';
-        $tmpDirectory = $this->filesystem->getDirectoryWrite(\Magento\Framework\App\Filesystem\DirectoryList::SYS_TMP);
+        $tmpDirectory = $this->filesystem->getDirectoryWrite(DirectoryList::SYS_TMP);
         $filePath = $tmpDirectory->getAbsolutePath($fileName);
         // phpcs:disable
         $file = fopen($filePath, "wb");
diff --git a/lib/internal/Magento/Framework/File/Mime.php b/lib/internal/Magento/Framework/File/Mime.php
index 148f43d47cfd4..e0b22e4c944d9 100644
--- a/lib/internal/Magento/Framework/File/Mime.php
+++ b/lib/internal/Magento/Framework/File/Mime.php
@@ -108,6 +108,9 @@ public function getMimeType($file)
 
         if (function_exists('mime_content_type')) {
             $result = $this->getNativeMimeType($file);
+        } else {
+            $imageInfo = getimagesize($file);
+            $result = $imageInfo['mime'];
         }
 
         if (null === $result && isset($this->mimeTypes[$extension])) {
diff --git a/lib/internal/Magento/Framework/File/Test/Unit/MimeTest.php b/lib/internal/Magento/Framework/File/Test/Unit/MimeTest.php
index 3c571452d7a3e..7a54a7966b500 100644
--- a/lib/internal/Magento/Framework/File/Test/Unit/MimeTest.php
+++ b/lib/internal/Magento/Framework/File/Test/Unit/MimeTest.php
@@ -58,6 +58,7 @@ public function getMimeTypeDataProvider(): array
             'weird extension' => [__DIR__ . '/_files/file.weird', 'application/octet-stream'],
             'weird uppercase extension' => [__DIR__ . '/_files/UPPERCASE.WEIRD', 'application/octet-stream'],
             'generic mime type' => [__DIR__ . '/_files/blank.html', 'text/html'],
+            'tmp file mime type' => [__DIR__ . '/_files/magento', 'image/jpeg'],
         ];
     }
 }
diff --git a/lib/internal/Magento/Framework/File/Test/Unit/_files/magento b/lib/internal/Magento/Framework/File/Test/Unit/_files/magento
new file mode 100644
index 0000000000000..c377daf8fb0b3
Binary files /dev/null and b/lib/internal/Magento/Framework/File/Test/Unit/_files/magento differ