<?php

/**
 * Drupal 7
 */
$fid = 1;
$uri = file_load($fid)->uri; // or fetched via the uri property of a field 
$image_url = image_style_url('thumbnail', $uri); 
$image = theme_image(array(
    'path' => $image_url,
    'alt' => 'my alt',
    'title' => 'my title',
    'attributes' => array(
      'class' => 'my-image',
    ))
);

/**
 * Drupal 8
 * @see http://www.vdmi.nl/blog/drupal-8-rendering-image-programmatically
 */
$file = File::load(1);
$variables = array(
  'style_name' => 'thumbnail',
  'uri' => $file->getFileUri(),
);

// The image.factory service will check if our image is valid.
$image = \Drupal::service('image.factory')->get($file->getFileUri());
if ($image->isValid()) {
  $variables['width'] = $image->getWidth();
  $variables['height'] = $image->getHeight();
}
else {
  $variables['width'] = $variables['height'] = NULL;
}

$logo_render_array = [
  '#theme' => 'image_style',
  '#width' => $variables['width'],
  '#height' => $variables['height'],
  '#style_name' => $variables['style_name'],
  '#uri' => $variables['uri'],
];

// Add the file entity to the cache dependencies.
// This will clear our cache when this entity updates.
$renderer = \Drupal::service('renderer');
$renderer->addCacheableDependency($logo_render_array, $file);