Since version ARRM 2.0.3.9 beta 2, it's possible to use scripts to generate artwork. (thank you by smashingblargharghar)

You can create your own scripts, drawing inspiration from those already available. It uses ImageMagick, which is already installed with ARRM.

To apply a script to ROMs that already have media, simply select your ROMs and click the Image Magick Scripts button in the Selected ROMs tab.

A window will open; select the desired script and click Run Script.

These scripts are a mix of Windows Batch and Image Magick-specific commands.

MAGICK: Path to magick.exe (do not modify)
SYSTEM_ROM_FOLDER: Example: e:\share\roms\fbneo
FILENAME: If the Image as ROM checkbox is checked, this variable will take The filename without extension is used as the value; otherwise, it will use the game name.
FILENAMEWITHOUTEXTENSION: Filename without extension
FILENAMEWITHEXTENSION: Filename with extension
GAMENAME: Game title

Full path to retrieved media ARRM

BEZEL
BOXART
BOXBACK
CARTRIDGE
EXTRA1
FANART
IMAGE
MAGAZINE
MANUAL
MAPS
MARQUEE
MIX
ROUNDWHEEL
SCREENSHOT
THUMBNAIL
TITLESHOT
VIDEO
WHEEL

Below is the full path to the media folder:

Example FOLDER_BOXART: e:\share\roms\fbneo\media\boxart (depending on your configuration) ARRM)

FOLDER_BEZEL
FOLDER_BOXART
FOLDER_BOXBACK
FOLDER_CARTRIDGE
FOLDER_EXTRA1
FOLDER_FANART
FOLDER_IMAGE
FOLDER_MAGAZINE
FOLDER_MANUAL
FOLDER_MAPS
FOLDER_MARQUEE
FOLDER_MIX
FOLDER_ROUNDWHEEL
FOLDER_SCREENSHOT
FOLDER_THEMEBUILDER
FOLDER_THUMBNAIL
FOLDER_TITLESHOT
FOLDER_VIDEO
FOLDER_WHEEL

Below you will find the suffix to use for your media:
Example SUFFIX_BOXART: -boxart (depending on your configuration) ARRM)

SUFFIX_BEZEL
SUFFIX_BOXART
SUFFIX_BOXBACK
SUFFIX_CARTRIDGE
SUFFIX_EXTRA1
SUFFIX_FANART
SUFFIX_IMAGE
SUFFIX_MAGAZINE
SUFFIX_MANUAL
SUFFIX_MAPS
SUFFIX_MARQUEE
SUFFIX_MIX
SUFFIX_ROUNDWHEEL
SUFFIX_SCREENSHOT
SUFFIX_THUMBNAIL
SUFFIX_TITLESHOT
SUFFIX_VIDEO
SUFFIX_WHEEL