Add watermark with CarrierWave

process :watermark

def watermark
second_image = MiniMagick::Image.open("https://s3.amazonaws.com/....logo.png")
manipulate! do |img|
  result = img.composite(second_image) do |c|
    c.compose "Over"    # OverCompositeOp
    c.gravity "Southeast" # copy second_image onto first_image from (20, 20)
  end
  result
  end
 end

# Process files as they are uploaded:
process :resize_to_fill => [850, 315]
process :convert => 'png'
process :watermark

def watermark
  manipulate! do |img|
    logo = Magick::Image.read("#{Rails.root}/app/assets/images/watermark.png").first
    img = img.composite(logo, Magick::NorthWestGravity, 15, 0, Magick::OverCompositeOp)
  end
end