example.module

<?php
 /**
 * @file
 *
 * @see http://drupal.org/user/413429
 */


function hook_block_view($delta = '') {

  $block = array();  // <-- this is a render array also!

  switch ($delta) {
    case 'foo':

      $block['content'] = array();

      // This is a render array the theme function theme_image_style will be called on somewhere in the theme wenn
      // it will be rendered by drupal_render() or render()
      $block['content']['myfirstimage'] = array(
        '#theme' => 'image_style',
        '#style_name' => 'full',   // <--- image style for thumbnail creation you create it in image style settings
        '#path' => drupal_get_path('module', 'mymodule') . '/images/image1',  // Path to original image (only a example)
      );

      $block['content']['mysecondimage'] = array(
        '#theme' => 'image_style',
        '#style_name' => 'full',   // <--- image style for thumbnail creation you create it in image style settings
        '#path' => drupal_get_path('module', 'mymodule') . '/images/image1',  // Path to original image (only a example)
      );

      break;
  }

  return $block;
}