diff --git a/core/modules/image/image.module b/core/modules/image/image.module
index ac12e54..924fb8e 100644
--- a/core/modules/image/image.module
+++ b/core/modules/image/image.module
@@ -1197,6 +1197,8 @@ function theme_image_style($variables) {
   $variables['width'] = $dimensions['width'];
   $variables['height'] = $dimensions['height'];
 
+  $variables['attributes']['class'][] = 'image-style-' . drupal_html_class($variables['style_name']);
+
   // Determine the url for the styled image.
   $variables['uri'] = image_style_url($variables['style_name'], $variables['uri']);
   return theme('image', $variables);
diff --git a/core/modules/image/lib/Drupal/image/Tests/ImageDimensionsTest.php b/core/modules/image/lib/Drupal/image/Tests/ImageDimensionsTest.php
index 0d57e11..ce1c247 100644
--- a/core/modules/image/lib/Drupal/image/Tests/ImageDimensionsTest.php
+++ b/core/modules/image/lib/Drupal/image/Tests/ImageDimensionsTest.php
@@ -65,7 +65,7 @@ class ImageDimensionsTest extends WebTestBase {
 
     image_effect_save('test', $effect);
     $img_tag = theme_image_style($variables);
-    $this->assertEqual($img_tag, '<img src="' . $url . '" width="120" height="60" alt="" />');
+    $this->assertEqual($img_tag, '<img class="image-style-test" src="' . $url . '" width="120" height="60" alt="" />');
     $this->assertFalse(file_exists($generated_uri), t('Generated file does not exist.'));
     $this->drupalGet($url);
     $this->assertResponse(200, t('Image was generated at the URL.'));
@@ -86,7 +86,7 @@ class ImageDimensionsTest extends WebTestBase {
 
     image_effect_save('test', $effect);
     $img_tag = theme_image_style($variables);
-    $this->assertEqual($img_tag, '<img src="' . $url . '" width="60" height="120" alt="" />');
+    $this->assertEqual($img_tag, '<img class="image-style-test" src="' . $url . '" width="60" height="120" alt="" />');
     $this->assertFalse(file_exists($generated_uri), t('Generated file does not exist.'));
     $this->drupalGet($url);
     $this->assertResponse(200, t('Image was generated at the URL.'));
@@ -108,7 +108,7 @@ class ImageDimensionsTest extends WebTestBase {
 
     image_effect_save('test', $effect);
     $img_tag = theme_image_style($variables);
-    $this->assertEqual($img_tag, '<img src="' . $url . '" width="45" height="90" alt="" />');
+    $this->assertEqual($img_tag, '<img class="image-style-test" src="' . $url . '" width="45" height="90" alt="" />');
     $this->assertFalse(file_exists($generated_uri), t('Generated file does not exist.'));
     $this->drupalGet($url);
     $this->assertResponse(200, t('Image was generated at the URL.'));
@@ -130,7 +130,7 @@ class ImageDimensionsTest extends WebTestBase {
 
     image_effect_save('test', $effect);
     $img_tag = theme_image_style($variables);
-    $this->assertEqual($img_tag, '<img src="' . $url . '" width="45" height="90" alt="" />');
+    $this->assertEqual($img_tag, '<img class="image-style-test" src="' . $url . '" width="45" height="90" alt="" />');
     $this->assertFalse(file_exists($generated_uri), t('Generated file does not exist.'));
     $this->drupalGet($url);
     $this->assertResponse(200, t('Image was generated at the URL.'));
@@ -148,7 +148,7 @@ class ImageDimensionsTest extends WebTestBase {
 
     image_effect_save('test', $effect);
     $img_tag = theme_image_style($variables);
-    $this->assertEqual($img_tag, '<img src="' . $url . '" width="45" height="90" alt="" />');
+    $this->assertEqual($img_tag, '<img class="image-style-test" src="' . $url . '" width="45" height="90" alt="" />');
     $this->assertFalse(file_exists($generated_uri), t('Generated file does not exist.'));
     $this->drupalGet($url);
     $this->assertResponse(200, t('Image was generated at the URL.'));
@@ -169,7 +169,7 @@ class ImageDimensionsTest extends WebTestBase {
 
     image_effect_save('test', $effect);
     $img_tag = theme_image_style($variables);
-    $this->assertEqual($img_tag, '<img src="' . $url . '" alt="" />');
+    $this->assertEqual($img_tag, '<img class="image-style-test" src="' . $url . '" alt="" />');
     $this->assertFalse(file_exists($generated_uri), t('Generated file does not exist.'));
     $this->drupalGet($url);
     $this->assertResponse(200, t('Image was generated at the URL.'));
@@ -189,7 +189,7 @@ class ImageDimensionsTest extends WebTestBase {
 
     image_effect_save('test', $effect);
     $img_tag = theme_image_style($variables);
-    $this->assertEqual($img_tag, '<img src="' . $url . '" width="30" height="30" alt="" />');
+    $this->assertEqual($img_tag, '<img class="image-style-test" src="' . $url . '" width="30" height="30" alt="" />');
     $this->assertFalse(file_exists($generated_uri), t('Generated file does not exist.'));
     $this->drupalGet($url);
     $this->assertResponse(200, t('Image was generated at the URL.'));
@@ -210,7 +210,7 @@ class ImageDimensionsTest extends WebTestBase {
 
     $effect = image_effect_save('test', $effect);
     $img_tag = theme_image_style($variables);
-    $this->assertEqual($img_tag, '<img src="' . $url . '" alt="" />');
+    $this->assertEqual($img_tag, '<img class="image-style-test" src="' . $url . '" alt="" />');
     $this->assertFalse(file_exists($generated_uri), t('Generated file does not exist.'));
     $this->drupalGet($url);
     $this->assertResponse(200, t('Image was generated at the URL.'));
@@ -228,6 +228,6 @@ class ImageDimensionsTest extends WebTestBase {
 
     image_effect_save('test', $effect);
     $img_tag = theme_image_style($variables);
-    $this->assertEqual($img_tag, '<img src="' . $url . '" alt="" />');
+    $this->assertEqual($img_tag, '<img class="image-style-test" src="' . $url . '" alt="" />');
   }
 }
diff --git a/core/modules/image/lib/Drupal/image/Tests/ImageFieldDisplayTest.php b/core/modules/image/lib/Drupal/image/Tests/ImageFieldDisplayTest.php
index 2ae34d1..edcb511 100644
--- a/core/modules/image/lib/Drupal/image/Tests/ImageFieldDisplayTest.php
+++ b/core/modules/image/lib/Drupal/image/Tests/ImageFieldDisplayTest.php
@@ -100,10 +100,11 @@ class ImageFieldDisplayTest extends ImageFieldTestBase {
     // Ensure the derivative image is generated so we do not have to deal with
     // image style callback paths.
     $this->drupalGet(image_style_url('thumbnail', $image_uri));
-    $image_info['uri'] = image_style_path('thumbnail', $image_uri);
+    $image_info['uri'] = $image_uri;
     $image_info['width'] = 100;
     $image_info['height'] = 50;
-    $default_output = theme('image', $image_info);
+    $image_info['style_name'] = 'thumbnail';
+    $default_output = theme('image_style', $image_info);
     $this->drupalGet('node/' . $nid);
     $this->assertRaw($default_output, t('Image style thumbnail formatter displaying correctly on full node view.'));
 
@@ -154,11 +155,12 @@ class ImageFieldDisplayTest extends ImageFieldTestBase {
     // style.
     $node = node_load($nid, NULL, TRUE);
     $image_info = array(
-      'uri' => image_style_url('medium', file_load($node->{$field_name}[LANGUAGE_NOT_SPECIFIED][0]['fid'])->uri),
+      'uri' => file_load($node->{$field_name}[LANGUAGE_NOT_SPECIFIED][0]['fid'])->uri,
       'width' => 220,
       'height' => 110,
+      'style_name' => 'medium',
     );
-    $default_output = theme('image', $image_info);
+    $default_output = theme('image_style', $image_info);
     $this->assertRaw($default_output, t("Preview image is displayed using 'medium' style."));
 
     // Add alt/title fields to the image and verify that they are displayed.
diff --git a/core/modules/image/lib/Drupal/image/Tests/ImageThemeFunctionTest.php b/core/modules/image/lib/Drupal/image/Tests/ImageThemeFunctionTest.php
index 3c61596..ec7f650 100644
--- a/core/modules/image/lib/Drupal/image/Tests/ImageThemeFunctionTest.php
+++ b/core/modules/image/lib/Drupal/image/Tests/ImageThemeFunctionTest.php
@@ -53,7 +53,7 @@ class ImageThemeFunctionTest extends WebTestBase {
       ),
     );
     $rendered_element = render($element);
-    $expected_result = '<a href="' . base_path() . $path . '"><img src="' . $url . '" alt="" /></a>';
+    $expected_result = '<a href="' . base_path() . $path . '"><img class="image-style-test" src="' . $url . '" alt="" /></a>';
     $this->assertEqual($expected_result, $rendered_element, 'theme_image_formatter() correctly renders without title, alt, or path options.');
 
     // Link the image to a fragment on the page, and not a full URL.
@@ -64,7 +64,7 @@ class ImageThemeFunctionTest extends WebTestBase {
       'fragment' => $fragment,
     );
     $rendered_element = render($element);
-    $expected_result = '<a href="#' . $fragment . '"><img src="' . $url . '" alt="" /></a>';
+    $expected_result = '<a href="#' . $fragment . '"><img class="image-style-test" src="' . $url . '" alt="" /></a>';
     $this->assertEqual($expected_result, $rendered_element, 'theme_image_formatter() correctly renders a link fragment.');
   }
 
@@ -78,17 +78,17 @@ class ImageThemeFunctionTest extends WebTestBase {
     $original_uri = file_unmanaged_copy($file->uri, 'public://', FILE_EXISTS_RENAME);
 
     // Create a style.
-    image_style_save(array('name' => 'test'));
-    $url = image_style_url('test', $original_uri);
+    image_style_save(array('name' => 'image_test'));
+    $url = image_style_url('image_test', $original_uri);
 
     $path = $this->randomName();
     $element = array(
       '#theme' => 'image_style',
-      '#style_name' => 'test',
+      '#style_name' => 'image_test',
       '#uri' => $original_uri,
     );
     $rendered_element = render($element);
-    $expected_result = '<img src="' . $url . '" alt="" />';
+    $expected_result = '<img class="image-style-image-test" src="' . $url . '" alt="" />';
     $this->assertEqual($expected_result, $rendered_element, 'theme_image_style() renders an image correctly.');
   }