Main/resources/[carscripts]/jg-advancedgarages/vehicle_images

This is where you can add custom vehicle thumbnails. But first:

1. You must have this feature enabled in config.lua Config.ShowVehicleImages = true
2. All images must be a png and a small file size. Ideally a 16:9 aspect ratio too

Learn more: https://docs.jgscripts.com/advanced-garages/vehicle-images