Use non-filling resize on server side. Client does filling.

src/web.rs

@@ -73,6 +73,7 @@ fn album(lib: Library, id: String) -> Result<impl warp::Reply, warp::Rejection>
 struct ImageParams {
     w: Option<u32>,
     h: Option<u32>,
+    fill: Option<bool>,
 }
 
 fn image(
@@ -81,7 +82,11 @@ fn image(
     params: ImageParams,
 ) -> Result<impl warp::Reply, warp::Rejection> {
     // TODO(wathiede): add caching headers.
-    match lib.thumbnail(&media_items_id, (params.w, params.h)) {
+    match lib.thumbnail(
+        &media_items_id,
+        (params.w, params.h),
+        params.fill.unwrap_or(false),
+    ) {
         None => {
             warn!("Couldn't find original {}", &media_items_id);
             Err(warp::reject::not_found())