Hello there, here's definitely not a secret but recent plugin that lets you replace your resources including images.
It works like that:
- You install the plugin
- You write down the path of the folder in the plugin settings where you will save your new reduced in size files
- You copy your Joplin files in resource directory to the path you wrote in the settings
- You use some quality/size reducing tool to all file in that copied folder (could be done with images in bulk via RawTherapee or lightroom)
- You click "Replace resources" from tool menu in Joplin
- Done, your new files are now in Joplin and will be synced with the cloud.
The advantages of this method:
- Works in bulk of any size
- Works with any file format
- Once setup you can run it multiple times: periodically (every sync) or until you get the result you need
- There's less risk messing data due to user error