layout_picker_custom_control.php

<?php
if (class_exists('WP_Customize_Control'))
{
    /**
     * Class to create a custom layout control
     */
    class Layout_Picker_Custom_control extends WP_Customize_Control
    {
          /**
           * Render the content on the theme customizer page
           */
          public function render_content()
           {

                ?>
                    <label>
                      <span class="customize-layout-control"><?php echo esc_html( $this->label ); ?></span>
                      <ul>
                        <li><img src="/img/1col.png" alt="Full Width" /><input type="radio" name="<?php echo $this->id; ?>" id="<?php echo $this->id; ?>[full_width]" value="1" /></li>
                        <li><img src="/img/2cl.png" alt="Left Sidebar" /><input type="radio" name="<?php echo $this->id; ?>" id="<?php echo $this->id; ?>[left_sidebar]" value="1" /></li>
                        <li><img src="/img/2cr.png" alt="Right Sidebar" /><input type="radio" name="<?php echo $this->id; ?>" id="<?php echo $this->id; ?>[right_sidebar]" value="1" /></li>
                      </ul>
                    </label>
                <?php
           }
    }
}
?>