diff --git a/README.md b/README.md
index ffc93456..45d454f3 100644
Binary files a/README.md and b/README.md differ
diff --git a/includes/shared.php b/includes/shared.php
index b39e0115..6c5fb144 100644
--- a/includes/shared.php
+++ b/includes/shared.php
@@ -4,7 +4,7 @@ define('AOWOW_REVISION', 19);
 define('CLI', PHP_SAPI === 'cli');
 
 
-$reqExt = ['SimpleXML', 'gd', 'mysqli', 'mbstring'];
+$reqExt = ['SimpleXML', 'gd', 'mysqli', 'mbstring', 'fileinfo'];
 $error  = '';
 foreach ($reqExt as $r)
     if (!extension_loaded($r))
diff --git a/pages/screenshot.php b/pages/screenshot.php
index e4c68ec2..4b5fbe77 100644
--- a/pages/screenshot.php
+++ b/pages/screenshot.php
@@ -299,23 +299,19 @@ class ScreenshotPage extends GenericPage
             return Lang::main('intError');
         }
 
+        // check if file is an image; allow jpeg, png
+        $finfo = new finfo(FILEINFO_MIME);                  // fileInfo appends charset information and other nonsense
+        $mime  = $finfo->file($_FILES['screenshotfile']['tmp_name']);
+        if (preg_match('/^image\/(png|jpe?g)/i', $mime, $m))
+            $isPNG = $m[0] == 'image/png';
+        else
+            return Lang::screenshot('error', 'unkFormat');
+
         // invalid file
         $is = getimagesize($_FILES['screenshotfile']['tmp_name']);
-        if (!$is || empty($is['mime']))
+        if (!$is)
             return Lang::screenshot('error', 'selectSS');
 
-        // allow jpeg, png
-        switch ($is['mime'])
-        {
-            case 'image/png':
-                $isPNG = true;
-            case 'image/jpg':
-            case 'image/jpeg':
-                break;
-            default:
-                return Lang::screenshot('error', 'unkFormat');
-        }
-
         // size-missmatch: 4k UHD upper limit; 150px lower limit
         if ($is[0] < $this->minSize || $is[1] < $this->minSize)
             return Lang::screenshot('error', 'tooSmall');