diff --git a/lib/camo/image.ex b/lib/camo/image.ex
index 6157515a..b0d495fe 100644
--- a/lib/camo/image.ex
+++ b/lib/camo/image.ex
@@ -5,7 +5,7 @@ defmodule Camo.Image do
     if !host or String.ends_with?(host, cdn_host()) do
       input
     else
-      camo_digest = :crypto.hmac(:sha, camo_key(), input) |> Base.encode16()
+      camo_digest = :crypto.hmac(:sha, camo_key(), input) |> Base.encode16(case: :lower)
       camo_uri = %URI{
         host: camo_host(),
         path: "/" <> camo_digest,