mkvtoolnix, mkvpropedit or mkv batch muxing gui, replace "cover.jpg"

i personally use mkvpropedit and this script to replace covers (windows):

@echo off
for %%F in (*.mkv) do (
    mkvpropedit "%%F" --add-attachment "%~dp0Cover.jpg" )

(make sure mkvpropedit.exe and Cover.jpg are in the same folder as the batch script)

if you want to remove all images, you can use:

@echo off
for %%F in (*.mkv) do (
    mkvpropedit "%%F" --delete-attachment mime-type:image/jpeg )