diff --git a/epub.php b/epub.php
index 1498cee..dfb7ed2 100644
--- a/epub.php
+++ b/epub.php
@@ -112,6 +112,8 @@
 						$imageid = $image->ContentItemId;
 						$imageurl = preg_replace('/GetPublicationContentItems-.*\.json/', 'Image-MEDIUM-' . $imageid . '.jpg', $url);
 
+						// Download image from source, put it in temp and include it into article main html content.
+						// Then pass true to last AddPage param to download image to epub.
 						$tempimgpath = './temp/' . $imageid . '.jpg';
 						$tempcontent = file_get_contents($imageurl);
 						file_put_contents($tempimgpath, $tempcontent);