diff --git a/README.md b/README.md
index ce50d4b..62dcda4 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,29 @@
 UIImage-ImagePickerCrop
 =======================
 
-Category on UIImage to create full-resolution cropped image from UIImagePickerController info dictionary
+Category on UIImage to create full-resolution cropped image from UIImagePickerController info dictionary.
+
+Background
+----------
+
+The `UIImagePickerController` class includes a parameter (`allowsEditing`) that
+lets the user move and scale the image and crop it to a square shape.
+
+The `info` dictionary returned as part of the `UIImagePickerControllerDelegate`
+protocol includes an "edited" version of the image, but its resolution is
+limited to a relatively small size.
+
+However, the dictionary also contains a pointer to the full-resolution image
+along with the the value for the `UIImagePickerControllerCropRect` key, which is
+a `CGRect` corresponding to the area selected by the user.
+
+Unfortunately grabbing a chunk of a UIImage from the device camera is not
+completely trivial, as the image data is always stored in the device's native
+orientation with a flag indicating that it should be rotated before being
+displayed.
+
+So a bit of low-level CoreGraphics-fu is required to rotate and translate the
+image before selecting the relevant area and drawing it to a CGContext.
+
+This category on UIImage does that in order to create a cropped image at the
+maximum possible resolution.