diff --git a/core/modules/image/image.module b/core/modules/image/image.module
index 4d7b967..0cff6bc 100644
--- a/core/modules/image/image.module
+++ b/core/modules/image/image.module
@@ -1160,8 +1160,10 @@ function image_effect_apply($image, $effect) {
  *   An associative array containing:
  *   - style_name: The name of the style to be used to alter the original image.
  *   - uri: The path of the image file relative to the Drupal files directory.
- *     This function does not work with images outside the files directory nor
- *     with remotely hosted images.
+ *   This function does not work with images outside the files directory nor
+ *   with remotely hosted images. This should be in a format such as
+ *   'images/image.jpg', or using a stream wrapper such as
+ *   'public://images/image.jpg'.
  *   - width: The width of the source image (if known).
  *   - height: The height of the source image (if known).
  *   - alt: The alternative text for text-based browsers.