Add captcha image generation functionality.

app/Captcha/Contracts/ImageBody.php

@@ -0,0 +1,12 @@
+<?php declare(strict_types=1);
+
+namespace App\Captcha\Contracts;
+
+use App\Captcha\Config\ImageBody as ImageBodyConfig;
+use App\Captcha\Dto\ImageBody as ImageBodyDto;
+use App\Captcha\Dto\Symbols;
+
+interface ImageBody
+{
+    public function processing(Symbols $symbols, ImageBodyConfig $config): ImageBodyDto;
+}