Fix ImageMagick 7+ warning (command 'convert' is deprecated)

[Jerry-Terrasse]

Reason

When using ImageMagick newer than 7.0, it give a WARNING: The convert command is deprecated in IMv7, use "magick", which means we should to use magick instead of convert.

Change

The script now dynamically checks for the presence of the magick command. If detected, it sets a variable to use magick instead of convert. This approach ensures compatibility with both newer and older versions of ImageMagick, eliminating deprecation warnings and maintaining functionality across different system setups.