: Open your file in MKVToolNix , go to the Attachments tab, and add your image. Label it cover.jpg or poster.jpg .
Once you have your image file (JPEG or PNG), you can "attach" it directly to the .mkv file so it shows up as a thumbnail in Windows Explorer or macOS Finder: Dolls (1987) PL.mkv
: Some players allow you to right-click the file and "Add Cover Art" or "Edit Metadata". 4. Suggested Folder Structure : Open your file in MKVToolNix , go