diff --git a/Gemfile b/Gemfile
index 10c92db..9a95876 100644
--- a/Gemfile
+++ b/Gemfile
@@ -26,8 +26,8 @@ gem "bootsnap", require: false
 # Add HTTP asset caching/compression and X-Sendfile acceleration to Puma [https://github.com/basecamp/thruster/]
 gem "thruster", require: false
 
-# Use Active Storage variants [https://guides.rubyonrails.org/active_storage_overview.html#transforming-images]
-# gem "image_processing", "~> 1.2"
+# Used to convert images into AVIF encoding.
+gem "image_processing", "~> 1.2"
 
 group :development, :test do
   # See https://guides.rubyonrails.org/debugging_rails_applications.html#debugging-with-the-debug-gem
diff --git a/Gemfile.lock b/Gemfile.lock
index d7397da..3cc1272 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -170,6 +170,14 @@ GEM
       multipart-post (~> 2.0)
     faraday-net_http (3.4.4)
       net-http (~> 0.5)
+    ffi (1.17.4-aarch64-linux-gnu)
+    ffi (1.17.4-aarch64-linux-musl)
+    ffi (1.17.4-arm-linux-gnu)
+    ffi (1.17.4-arm-linux-musl)
+    ffi (1.17.4-arm64-darwin)
+    ffi (1.17.4-x86_64-darwin)
+    ffi (1.17.4-x86_64-linux-gnu)
+    ffi (1.17.4-x86_64-linux-musl)
     fiddle (1.1.8)
     fugit (1.13.0)
       et-orbi (~> 1.4)
@@ -187,6 +195,9 @@ GEM
     high_voltage (5.0.0)
     i18n (1.15.2)
       concurrent-ruby (~> 1.0)
+    image_processing (1.14.0)
+      mini_magick (>= 4.9.5, < 6)
+      ruby-vips (>= 2.0.17, < 3)
     io-console (0.9.2)
     irb (1.18.0)
       pp (>= 0.6.0)
@@ -226,6 +237,8 @@ GEM
     marcel (1.2.1)
     matrix (0.4.3)
     method_source (1.1.0)
+    mini_magick (5.4.0)
+      logger
     mini_mime (1.1.5)
     minitest (6.0.6)
       drb (~> 2.0)
@@ -424,6 +437,9 @@ GEM
       rubocop-performance (>= 1.24)
       rubocop-rails (>= 2.30)
     ruby-progressbar (1.13.0)
+    ruby-vips (2.3.0)
+      ffi (~> 1.12)
+      logger
     rubyzip (3.6.0)
     securerandom (0.4.1)
     selenium-webdriver (4.49.0)
@@ -535,6 +551,7 @@ DEPENDENCIES
   faraday-follow_redirects
   hashid-rails
   high_voltage
+  image_processing (~> 1.2)
   jb
   kaminari
   lockbox
diff --git a/app/components/uploads/index.rb b/app/components/uploads/index.rb
index 820d9ea..77e5c7b 100644
--- a/app/components/uploads/index.rb
+++ b/app/components/uploads/index.rb
@@ -36,9 +36,24 @@ def header_section
         end
       end
 
-      label(for: "dropzone-file-input", class: "btn btn-primary", style: "cursor: pointer;") do
-        render Primer::Beta::Octicon.new(icon: :upload, mr: 1)
-        plain "Upload Files"
+      div(style: "display: flex; flex-direction: column; align-items: flex-end; gap: 6px;") do
+        label(for: "dropzone-file-input", class: "btn btn-primary", style: "cursor: pointer;") do
+          render Primer::Beta::Octicon.new(icon: :upload, mr: 1)
+          plain "Upload Files"
+        end
+
+        label(for: "auto-convert-avif", style: "display: flex; align-items: center; gap: 6px; font-size: 13px; color: var(--fgColor-muted, #656d76); cursor: pointer;") do
+          input(
+            type: "checkbox",
+            name: "convert_to_avif",
+            value: "1",
+            id: "auto-convert-avif",
+            form: "dropzone-upload-form",
+            checked: true,
+            style: "cursor: pointer;"
+          )
+          plain "Auto-convert images to AVIF"
+        end
       end
     end
   end
@@ -125,7 +140,7 @@ def pagination_section
   end
 
   def dropzone_form
-    form_with url: uploads_path, method: :post, multipart: true, data: { dropzone_form: true } do
+    form_with url: uploads_path, method: :post, multipart: true, id: "dropzone-upload-form", data: { dropzone_form: true } do
       input(type: "file", name: "files[]", id: "dropzone-file-input", multiple: true, data: { dropzone_input: true }, style: "display: none;")
     end
   end
diff --git a/app/controllers/uploads_controller.rb b/app/controllers/uploads_controller.rb
index 157ac29..aca6f41 100644
--- a/app/controllers/uploads_controller.rb
+++ b/app/controllers/uploads_controller.rb
@@ -26,7 +26,11 @@ def create
       return
     end
 
-    service = BatchUploadService.new(user: current_user, provenance: :web)
+    service = BatchUploadService.new(
+      user: current_user,
+      provenance: :web,
+      convert_to_avif: params[:convert_to_avif] == "1"
+    )
     result = service.process_files(uploaded_files)
 
     flash_message = build_flash_message(result)
diff --git a/app/services/batch_upload_service.rb b/app/services/batch_upload_service.rb
index 2bcc339..7a114fb 100644
--- a/app/services/batch_upload_service.rb
+++ b/app/services/batch_upload_service.rb
@@ -6,9 +6,10 @@ class BatchUploadService
   Result = Data.define(:uploads, :failed)
   FailedUpload = Data.define(:filename, :reason)
 
-  def initialize(user:, provenance:)
+  def initialize(user:, provenance:, convert_to_avif: false)
     @user = user
     @provenance = provenance
+    @convert_to_avif = convert_to_avif
     @quota_service = QuotaService.new(user)
     @policy = @quota_service.current_policy
   end
@@ -126,16 +127,27 @@ def create_upload(file)
                    file.content_type ||
                    "application/octet-stream"
     content_type = Upload.normalize_content_type(content_type)
+    converted_file = nil
+
+    if @convert_to_avif && content_type.start_with?("image/") && content_type != "image/avif"
+      converted_file = convert_to_avif(file)
+      converted_file = nil if converted_file.size > @policy.max_file_size
+    end
+
+    filename = converted_file ? avif_filename(file.original_filename) : file.original_filename
+    io = converted_file || file.tempfile
+    content_type = "image/avif" if converted_file
 
     upload_id = SecureRandom.uuid_v7
-    sanitized_filename = ActiveStorage::Filename.new(file.original_filename).sanitized
+    sanitized_filename = ActiveStorage::Filename.new(filename).sanitized
     storage_key = "#{upload_id}/#{sanitized_filename}"
 
     blob = ActiveStorage::Blob.create_and_upload!(
-      io: file.tempfile,
-      filename: file.original_filename,
+      io: io,
+      filename: filename,
       content_type: content_type,
-      key: storage_key
+      key: storage_key,
+      identify: false
     )
 
     @user.uploads.create!(
@@ -143,6 +155,21 @@ def create_upload(file)
       blob: blob,
       provenance: @provenance
     )
+  ensure
+    converted_file&.close!
+  end
+
+  def convert_to_avif(file)
+    ImageProcessing::Vips
+      .source(file.tempfile.path)
+      .convert(:avif)
+      .saver(Q: 80)
+      .call
+  end
+
+  def avif_filename(filename)
+    extension = File.extname(filename)
+    extension.present? ? "#{filename.delete_suffix(extension)}.avif" : "#{filename}.avif"
   end
 
   def human_size(bytes)
diff --git a/test/controllers/uploads_batch_test.rb b/test/controllers/uploads_batch_test.rb
index 54b9255..e3910d6 100644
--- a/test/controllers/uploads_batch_test.rb
+++ b/test/controllers/uploads_batch_test.rb
@@ -21,6 +21,13 @@ def create_upload_for(user, filename: "existing.png")
 
   # --- batch upload ---
 
+  test "shows the AVIF conversion checkbox enabled by default" do
+    get uploads_url
+
+    assert_response :success
+    assert_select 'input[name="convert_to_avif"][checked]'
+  end
+
   test "uploads multiple files in one request" do
     files = [ fixture_file_upload("test.png", "image/png"), fixture_file_upload("test.png", "image/png") ]
 
@@ -32,6 +39,18 @@ def create_upload_for(user, filename: "existing.png")
     assert_match(/Uploaded 2 files/, flash[:notice])
   end
 
+  test "passes the AVIF conversion choice for an uploaded image" do
+    post uploads_url, params: {
+      files: [ fixture_file_upload("test.png", "image/png") ],
+      convert_to_avif: "1"
+    }
+
+    assert_redirected_to uploads_path
+    upload = Upload.order(:created_at).last
+    assert_equal "test.avif", upload.filename.to_s
+    assert_equal "image/avif", upload.content_type
+  end
+
   test "still accepts a single legacy file param" do
     assert_difference("Upload.count", 1) do
       post uploads_url, params: { file: fixture_file_upload("test.png", "image/png") }
diff --git a/test/services/batch_upload_service_test.rb b/test/services/batch_upload_service_test.rb
index d191770..2678d1d 100644
--- a/test/services/batch_upload_service_test.rb
+++ b/test/services/batch_upload_service_test.rb
@@ -24,8 +24,12 @@ def uploaded_file(name, size)
     )
   end
 
-  def service
-    BatchUploadService.new(user: @user, provenance: :web)
+  def service(convert_to_avif: false)
+    BatchUploadService.new(
+      user: @user,
+      provenance: :web,
+      convert_to_avif: convert_to_avif
+    )
   end
 
   test "uploads every file when the whole batch fits in quota" do
@@ -40,6 +44,26 @@ def service
     assert_empty result.failed
   end
 
+  test "converts supported images to AVIF when requested" do
+    image = Rack::Test::UploadedFile.new(file_fixture("test.png").to_path, "image/png", true)
+    result = service(convert_to_avif: true).process_files([ image ])
+    upload = result.uploads.sole
+
+    assert_empty result.failed
+    assert_equal "test.avif", upload.filename.to_s
+    assert_equal "image/avif", upload.content_type
+  end
+
+  test "leaves images unchanged when AVIF conversion is disabled" do
+    image = Rack::Test::UploadedFile.new(file_fixture("test.png").to_path, "image/png", true)
+    result = service.process_files([ image ])
+    upload = result.uploads.sole
+
+    assert_empty result.failed
+    assert_equal "test.png", upload.filename.to_s
+    assert_equal "image/png", upload.content_type
+  end
+
   test "rejects a file larger than the per-file limit without uploading it" do
     files = [
       uploaded_file("ok.txt", 1.megabyte),