More dev notes

doc/README.DeveloperNotes.md

@@ -87,3 +87,25 @@ AppStream data
   user-generated: uploaded by a random user
   upstream: official screenshot from the developer
   logo: not a screenshot - just a logo
+
+---
+
+debshots used to use the 'paperclip' gem for file handling of images.
+Paperclip was deprecated so something new was needed. At the same time
+Rails 6.0 was released and offered file handling using ActiveStorage.
+However ActiveStorage was so seriously flawed and incomplete in 2020
+that I decided to go for the 'shrine' gem.
+
+There is a Rake task that converts Paperclip attachments to Shrine attachments.
+This is a one-time conversion.
+
+Images are saved in four ways:
+- original image
+- thumb image (to be used in packages.debian.org)
+- large image (original image with watermark on the right edge)
+- medium image (up to 800x600)
+- small image (up to 320x240) for gallery/grid views
+
+Screenshot.image was the Paperclip image attachment.
+Screenshot.simge is the Shring image attachment.
+I used two different attributes to avoid confusion.