If you are adding images and notes manually via the Anki app, this problem doesn’t occur. Anki automatically converts the filenames to lowercase when adding them to the media collection folder, and then it uses the lowercased names in the note fields.
If you are using some other method to add images and notes, I suspect that the easiest way to prevent the issue would be to change the filenames and/or the contents of the note fields before adding them.
But, if you don’t want to prevent the problem, I found some Add-ons that might help fix the problem after it occurs:
- Capitalize (uppercase/lowercase/titlecase) (bulk-capitalize or uncapitalize text in note fields)
- Text Field Transformer (Apply transformations to selected notes or all notes, Built-in types:
lower,upper,capitalize)