# values in this case:
# - columns: 4
# - rows: 3
# - dimensions: an array containing two numbers (potentially floats due to mm to pixels conversion)
# - picture_paths: an array of already cropped pictures
# - target_path: the target path (obviously)
`montage -tile #{columns}x#{rows} -geometry #{dimensions.join('x')}+0+0 #{picture_paths.join(' ')} #{target_path}`