diff --git a/index.d.ts b/index.d.ts
index a9dd5d8..16f3532 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -232,6 +232,10 @@ declare module looksSame {
          * Ability to ignore text caret
          */
         ignoreCaret?: boolean;
+        /**
+         * Defines what image type is created
+         */
+        extension?: string;
     }
 
     /**