added destroy method

src/Intervention/Image/Image.php

@@ -72,7 +72,7 @@ class Image
     /**
      * Attributes of the original created image
      *
-     * @var Array
+     * @var resource
      */
     protected $original;
 
@@ -1890,6 +1890,17 @@ class Image
         return $this->encoded;
     }
 
+    /**
+     * Destroys image resource and frees memory
+     *
+     * @return void
+     */
+    public function destroy()
+    {
+        is_resource($this->resource) ? imagedestroy($this->resource) : null;
+        is_resource($this->original) ? imagedestroy($this->original) : null;
+    }
+
     /**
      * Returns image stream
      *

tests/ImageTest.php

@@ -1784,4 +1784,11 @@ class ImageTest extends PHPUnit_Framework_Testcase
         $img->encode();
         $this->assertEquals($img->encoded, $img->encode());
     }
+
+    public function testDestroy()
+    {
+        $img = $this->getTestImage();
+        $img->destroy();
+        $this->assertEquals(get_resource_type($img->resource), 'Unknown');
+    }
 }