Refactoring with use of separate to sub classes from Image. Add FileHelper to trying toString conversion. Add ImageCollection (not tested work).

File.class.php

@@ -11,7 +11,6 @@ abstract class File
      */
     public static function getInstance($data)
     {
-        $instance = new static($data);
         if (is_null($data) || $data == '') {
             throw new ErrorException('Empty data for File::getInstance().');
         }
@@ -21,6 +20,7 @@ abstract class File
                 throw new ErrorException('Unable to convert json-string to array.');
             }
         }
+        $instance = new static($data);
         foreach ($data as $attribute_name => $attribute_value) {
             if (property_exists($instance, $attribute_name)) {
                 $instance->{$attribute_name} = $attribute_value;
@@ -30,6 +30,22 @@ abstract class File
     }
 
     /**
+     * @param $size string
+     * @return ImageVariant
+     */
+    public function getImageVariant($size)
+    {
+        if (!array_key_exists($size, $this->variants)) {
+            $this->variants[$size] = new ImageVariant;
+        } else {
+            if (!is_object($this->variants[$size])) {
+                $this->variants[$size] = parent::getInstance($this->variants[$size]);
+            }
+        }
+        return $this->variants[$size];
+    }
+
+    /**
      * @return string
      */
     public function getWebName()
@@ -39,15 +55,6 @@ abstract class File
 
     public function __toString()
     {
-        return self::toString($this);
-    }
-
-    private static function toString($class)
-    {
-        $data = array();
-        foreach ($class as $attribute_name => $attribute_value) {
-            $data[$attribute_name] = $attribute_value;
-        }
-        return json_encode($data);
+        return FileHelper::toString($this);
     }
 }

FileHelper.class.php

@@ -0,0 +1,13 @@
+<?php
+
+class FileHelper
+{
+    public static function toString($object)
+    {
+        $data = array();
+        foreach ($object as $attribute_name => $attribute_value) {
+            $data[$attribute_name] = $attribute_value;
+        }
+        return json_encode($data);
+    }
+}

Image.class.php

@@ -10,33 +10,27 @@ class Image extends File
     public $original_filename;
     public $variants = array();
 
-    const SIZE_100_80 = '100x80';
-    const SIZE_200_160 = '200x160';
-    const SIZE_300_240 = '300x240';
-    const SIZE_550_440 = '550x440';
-    const SIZE_SKI = 'x';
-    const SIZE_INSTRUCTION = 'x';
-
-    public static $sizes = array(
-        self::SIZE_100_80,
-        self::SIZE_200_160,
-        self::SIZE_300_240,
-        self::SIZE_550_440
-    );
+    protected $sizes;
 
     /**
-     * @param $size string
-     * @return Image
+     * @param $class string
+     * @throws ErrorException
      */
-    public function getVariant($size)
+    public static function checkSubClass($class)
     {
-        if (!array_key_exists($size, $this->variants)) {
-            $this->variants[$size] = new ImageVariant;
-        } else {
-            if (!is_object($this->variants[$size])) {
-                $this->variants[$size] = parent::getInstance($this->variants[$size]);
+        if (is_null($class) || $class == '') {
+            throw new ErrorException('Class not defined.');
+        }
+        if (!class_exists($class)) {
+            throw new ErrorException('Class "' . $class . '" not exists.');
+        }
+        if (get_parent_class($class) != 'Image') {
+            throw new ErrorException('Class "' . $class . '" mast be extend of "Image".');
         }
     }
-        return $this->variants[$size];
+
+    public function getSizes()
+    {
+        return $this->sizes;
     }
 }

ImageCollection.class.php

@@ -0,0 +1,34 @@
+<?php
+
+abstract class ImageCollection extends ArrayIterator
+{
+    /**
+     * @var string
+     */
+    protected $class;
+
+    /**
+     * @param array $data
+     * @throws ErrorException
+     */
+    public function __construct($data)
+    {
+        /**
+         * @var $class Image
+         */
+        $class = $this->class;
+        Image::checkSubClass($class);
+        if (is_null($data) || $data == '') {
+            throw new ErrorException('Empty data.');
+        }
+        if (!is_array($data)) {
+            $data = json_decode($data, true);
+            if (json_last_error() != JSON_ERROR_NONE) {
+                throw new ErrorException('Unable to convert json-string to array.');
+            }
+        }
+        foreach ($data as $item_data) {
+            $this->append($class::getInstance($item_data));
+        }
+    }
+}

Upload.class.php

@@ -11,27 +11,34 @@ abstract class Upload
         return $greagwar_image;
     }
     /**
+     * @param $class string
      * @param $file array (ex. ['tmp_name' => '...', 'name' => '...', 'type' => '...'])
      * @param $force_create_variants bool
      * @return Image
+     * @throws ErrorException
      */
-    public static function image($file, $force_create_variants = true)
+    public static function image($class, $file, $force_create_variants = true)
     {
-        $image = new Image;
+        /**
+         * @var $image Image
+         */
+        Image::checkSubClass($class);
+        $image = new $class;
         $image->original_filename = $file['name'];
         $greagwar_image = self::getGreagwarImage($file['tmp_name']);
         self::saveImage($image, $greagwar_image);
         if ($force_create_variants) {
-            foreach (Image::$sizes as $size) {
+            $sizes = $image->getSizes();
+            foreach ($sizes as $size) {
                 $size_parts = explode('x', $size);
-                self::saveImage($image->getVariant($size), $greagwar_image, $size_parts[0] ? : null, $size_parts[1] ? : null);
+                self::saveImage($image->getImageVariant($size), $greagwar_image, $size_parts[0] ? : null, $size_parts[1] ? : null);
             }
         }
         return $image;
     }
 
     /**
-     * @param $image Image
+     * @param $image ImageVariant
      * @param $greagwar_image GreagwarImage
      * @param null $width
      * @param null $height