--- attachments_controller.rb	2020-08-25 09:00:50.000000000 +0200
+++ inline_attachment_images.rb	2020-08-25 08:46:12.000000000 +0200
@@ -1,7 +1,16 @@
-  def disposition(attachment)
+module InlineAttachmentImages
+  private def disposition(attachment)
     if attachment.is_pdf?
       'inline'
+    elsif attachment.is_image?
+      'inline'
     else
       'attachment'
     end
   end
+end
+
+require_dependency 'attachments_controller'
+class ::AttachmentsController
+  prepend InlineAttachmentImages
+end