diff --git a/image-rs/src/pull.rs b/image-rs/src/pull.rs
index 5bbb91329..91e601148 100644
--- a/image-rs/src/pull.rs
+++ b/image-rs/src/pull.rs
@@ -470,7 +470,7 @@ mod tests {
 
         for image_url in nydus_images.iter() {
             let tempdir = tempfile::tempdir().unwrap();
-            let image = Reference::try_from((*image_url).clone()).expect("create reference failed");
+            let image = Reference::try_from(*image_url).expect("create reference failed");
             let mut client = PullClient::new(
                 image,
                 tempdir.path(),
diff --git a/image-rs/src/resource/mod.rs b/image-rs/src/resource/mod.rs
index 923d4e6a9..57945dc22 100644
--- a/image-rs/src/resource/mod.rs
+++ b/image-rs/src/resource/mod.rs
@@ -30,6 +30,7 @@ lazy_static::lazy_static! {
 /// - `SCHEME`: `file` string, to distinguish different uri scheme
 /// - `get_resource()`: get resource from the uri
 #[async_trait]
+#[allow(dead_code)]
 trait Protocol: Send + Sync {
     async fn get_resource(&mut self, uri: &str) -> Result<Vec<u8>>;
 }
diff --git a/image-rs/src/signature/image/digest.rs b/image-rs/src/signature/image/digest.rs
index 0b0d24d7e..a1313b720 100644
--- a/image-rs/src/signature/image/digest.rs
+++ b/image-rs/src/signature/image/digest.rs
@@ -76,9 +76,9 @@ impl Digest {
     }
 }
 
-impl ToString for Digest {
-    fn to_string(&self) -> String {
-        format!("{}:{}", self.algorithm, self.value)
+impl fmt::Display for Digest {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}:{}", self.algorithm, self.value)
     }
 }