core/themes/classy/templates/field/image.html.twig | 20 ++++++++++++++++++++
 core/themes/stable/templates/field/image.html.twig | 20 ++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/core/themes/classy/templates/field/image.html.twig b/core/themes/classy/templates/field/image.html.twig
index bfa1853..690e0d8 100644
--- a/core/themes/classy/templates/field/image.html.twig
+++ b/core/themes/classy/templates/field/image.html.twig
@@ -5,7 +5,27 @@
  * Theme override of an image.
  *
  * Available variables:
+ * - uri: Either the path of the image file (relative to base_path()) or a
+ *   full URL.
+ * - width: The width of the image (if known).
+ * - height: The height of the image (if known).
+ * - alt: The alternative text for text-based browsers. HTML 4 and XHTML 1.0
+ *   always require an alt attribute. The HTML 5 draft allows the alt
+ *   attribute to be omitted in some cases. Therefore, this variable defaults
+ *   to an empty string, but can be set to NULL for the attribute to be
+ *   omitted. Usually, neither omission nor an empty string satisfies
+ *   accessibility requirements, so it is strongly encouraged for code
+ *   building variables for image.html.twig templates to pass a meaningful
+ *   value for this variable.
+ *   - http://www.w3.org/TR/REC-html40/struct/objects.html#h-13.8
+ *   - http://www.w3.org/TR/xhtml1/dtds.html
+ *   - http://dev.w3.org/html5/spec/Overview.html#alt
+ * - title: The title text is displayed when the image is hovered in some
+ *   popular browsers.
  * - attributes: HTML attributes for the img tag.
+ * - srcset: Array of multiple URIs and sizes/multipliers.
+ * - sizes: The sizes attribute for viewport-based selection of images.
+ *   - http://www.whatwg.org/specs/web-apps/current-work/multipage/embedded-content.html#introduction-3:viewport-based-selection-2
  * - style_name: (optional) The name of the image style applied.
  */
 #}
diff --git a/core/themes/stable/templates/field/image.html.twig b/core/themes/stable/templates/field/image.html.twig
index 07aa2bf..71f1e20 100644
--- a/core/themes/stable/templates/field/image.html.twig
+++ b/core/themes/stable/templates/field/image.html.twig
@@ -5,7 +5,27 @@
  * Theme override of an image.
  *
  * Available variables:
+ * - uri: Either the path of the image file (relative to base_path()) or a
+ *   full URL.
+ * - width: The width of the image (if known).
+ * - height: The height of the image (if known).
+ * - alt: The alternative text for text-based browsers. HTML 4 and XHTML 1.0
+ *   always require an alt attribute. The HTML 5 draft allows the alt
+ *   attribute to be omitted in some cases. Therefore, this variable defaults
+ *   to an empty string, but can be set to NULL for the attribute to be
+ *   omitted. Usually, neither omission nor an empty string satisfies
+ *   accessibility requirements, so it is strongly encouraged for code
+ *   building variables for image.html.twig templates to pass a meaningful
+ *   value for this variable.
+ *   - http://www.w3.org/TR/REC-html40/struct/objects.html#h-13.8
+ *   - http://www.w3.org/TR/xhtml1/dtds.html
+ *   - http://dev.w3.org/html5/spec/Overview.html#alt
+ * - title: The title text is displayed when the image is hovered in some
+ *   popular browsers.
  * - attributes: HTML attributes for the img tag.
+ * - srcset: Array of multiple URIs and sizes/multipliers.
+ * - sizes: The sizes attribute for viewport-based selection of images.
+ *   - http://www.whatwg.org/specs/web-apps/current-work/multipage/embedded-content.html#introduction-3:viewport-based-selection-2
  * - style_name: (optional) The name of the image style applied.
  */
 #}