Write documentation for image optimization / compression feature

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## Version 1.3.0 (XXXXXXXXXX)
 
 - Optionally scale down large images within quiz reports to preserve space and keep PDF files compact
+- Optionally compress images within quiz reports to preserve space and keep PDF files compact
 - Fix image inlining for files with non-lowercase file extensions (e.g., `image.JPG`)
 - Fix conditional hide/show of retention time in quiz archive form when locked
 - Optimize order of settings in quiz archive form and plugin admin settings

README.md

@@ -422,6 +422,34 @@ Locked options will be grayed out during archive creation (8).
 [![Screenshot: Configuration - Archive job presets 3](doc/configuration/configuration_archive_job_presets_3_thumb.png)](doc/configuration/configuration_archive_job_presets_3.png)
 
 
+### Image optimization / compression
+
+If quizzes contain a large number of images or images with a excessively high
+resolutions (e.g., 4000x3000 px), the quiz archiver can compress such images
+during archiving. This can significantly reduce the size of the generated
+PDF files. HTML source files, if generated, are never modified and remain
+untouched.
+
+To enable image optimization for a quiz archive job:
+
+1. Navigate to the quiz archiver overview page
+2. Expand the _Advanced settings_ section of the _Create new quiz archive_ form
+3. Check the _Optimize images_ checkbox (1)
+4. Set the desired maximum dimensions and quality (2)
+   - If an image exceeds any of the specified dimensions, it will be resized
+     proportionally to fit within the specified bounds.
+   - The quality setting controls the compression level of the images. A value
+     of 100% will result in no compression, while a value of 0% will result in
+     the lowest quality and smallest file size. A value of 85% is a good
+     compromise between quality and file size.
+5. Continue with the archive creation as usual
+
+_Note: It is strongly advised to lock quality settings to global defaults using
+the [archive job presets](#archive-job-presets-global-defaults--policies)._
+
+[![Screenshot: Configuration - Image optimization](doc/configuration/configuration_job_image_optimization_thumb.png)](doc/configuration/configuration_job_image_optimization.png)
+
+
 ### Automatic deletion of quiz archives (retention policy)
 
 Quiz archives can be automatically deleted after a specified retention period.