diff --git a/src/library/entry.cr b/src/library/entry.cr
index 301c3ba..28b7122 100644
--- a/src/library/entry.cr
+++ b/src/library/entry.cr
@@ -40,7 +40,8 @@ class Entry
 
     file = ArchiveFile.new @zip_path
     @pages = file.entries.count do |e|
-      filename_is_image e.filename
+      SUPPORTED_IMG_TYPES.includes? \
+        MIME.from_filename? e.filename
     end
     file.close
   end
@@ -102,7 +103,8 @@ class Entry
     ArchiveFile.open @zip_path do |file|
       entries = file.entries
         .select { |e|
-          filename_is_image e.filename
+          SUPPORTED_IMG_TYPES.includes? \
+            MIME.from_filename? e.filename
         }
         .sort! { |a, b|
           compare_numerically a.filename, b.filename
diff --git a/src/library/types.cr b/src/library/types.cr
index a91ca86..a4de007 100644
--- a/src/library/types.cr
+++ b/src/library/types.cr
@@ -1,3 +1,5 @@
+SUPPORTED_IMG_TYPES = ["image/jpeg", "image/png", "image/webp"]
+
 enum SortMethod
   Auto
   Title
diff --git a/src/routes/api.cr b/src/routes/api.cr
index 80cb278..b1fb3b3 100644
--- a/src/routes/api.cr
+++ b/src/routes/api.cr
@@ -456,8 +456,9 @@ struct APIRouter
             entry_id = env.params.query["eid"]?
             title = Library.default.get_title(title_id).not_nil!
 
-            unless filename_is_image filename
-              raise "The uploaded file must be an image"
+            unless SUPPORTED_IMG_TYPES.includes? \
+                     MIME.from_filename? filename
+              raise "The uploaded image must be either JPEG or PNG"
             end
 
             ext = File.extname filename
diff --git a/src/util/util.cr b/src/util/util.cr
index 2db7457..c4e168a 100644
--- a/src/util/util.cr
+++ b/src/util/util.cr
@@ -120,7 +120,3 @@ class String
     match / s.size
   end
 end
-
-def filename_is_image(fn : String) : Bool
-  MIME.from_filename?(fn).try(&.starts_with?("image/")) || false
-end
diff --git a/src/views/title.html.ecr b/src/views/title.html.ecr
index dc0dc3d..78edf98 100644
--- a/src/views/title.html.ecr
+++ b/src/views/title.html.ecr
@@ -101,7 +101,7 @@
                 <span uk-icon="icon: cloud-upload"></span>
                 <span class="uk-text-middle">Upload a cover image by dropping it here or</span>
                 <div uk-form-custom>
-                  <input type="file" accept="image/*">
+                  <input type="file" accept="<%= SUPPORTED_IMG_TYPES.join ", " %>">
                   <span class="uk-link">selecting one</span>
                 </div>
               </div>